32.1: The Basics of Climate Change

Search Fundamentals of Biochemistry

Learning Objectives

• to demonstrate how climate has changed over geological time through the present 
• to explain mechanisms, using knowledge from biology, chemistry, and physics, for climate change
• to show the central role of atmospheric CO₂ as a causative agent of past and present climate change
• to contrast the effects of anthropogenic burning of fossil fuels on climate change with causes of past climate changes 
• to address arguments made by climate change skeptics

Introduction

We've known for a very long time that burning fossil fuels and releasing CO₂ into the atmosphere would warm our climate. Perhaps the first paper addressing this, Circumstances affecting the Heat of the Sun's Rays, was published in 1856, before the US Civil War, by a woman scientist, Eunice Foote. John Tyndall (of the Tyndall effect) published more comprehensively on greenhouse gases in 1859. Given the complexity of the biosphere's climate, it was not until the 1980s that climate models became sophisticated enough for scientists like James Hansen to become convinced and alarmed enough to discuss in Congressional hearings the role of anthropogenic (made by humans) CO₂ released into the atmosphere as a cause of ever-worsening global warming. The knowledge of human-induced climate change has been politicized and subjected to an orchestrated campaign of misinformation and disinformation by fossil fuel companies and their political contributors. We have delayed global actions for so long that we must act immediately and aggressively to address climate change before we reach climatic conditions that are so austere for humans that parts of the world become uninhabitable. Homo sapiens evolved in a world dominated by repetitive glaciation and deglaciation. Hans Joachim Schellnhuber, an atmospheric physicist, climatologist, and founding director of the Potsdam Institute for Climate Impact Research, has stated that humans have so affected the world that we have eliminated the possibility of the next glaciation cycle. 

Many readers might not be familiar with the data and models supporting human-caused climate change and that climate scientists are almost unanimous in their support of the data and models. As in any field, however, you will find outliers who don't and whose ideas carry disproportionate weight among climate change skeptics. Hence, we provide the basic data to show the relationship between increasing atmospheric CO₂ to global warming, both drought and flooding, ocean acidification, and loss of biodiversity.  We also provide supportive information that would allow users to address questions from those who question the reality of present human-induced climate change. We don't shy away from using basic physics as well since most students studying biochemistry at the level found in this book have also studied physics as well as biology. In subsequent sections, we will then address the biochemistry of climate change and its mitigation.

Green House Effect

Before the advent of the industrial revolution, the earth's climate was fairly constant since the last ice age, which peaked about 22,000 years ago (YA) and ended about 12,000 YA. There have been short (on a geological time scale) periods of cooling since the end of the last ice age. Humans evolved around 200,000 years ago with modern civilizations arising about 4000 BCE so it could be said that humans are ice-age peoples (a distinctly Northern Hemisphere perspective). Humans have had the benefits of a fairly stable climate since then.

The sun's energy warms the earth. If the earth did not radiate back into space an equivalent amount of energy, it would slowly and continually warm. The earth reflects energy back in the form of light. In addition, as the earth is heated by the sun, the earth releases heat in the form of infrared light (as do all warm objects). Earth's temperatures are stable when the sum of the energy emitted by the earth equals the energy it receives from the sun.  This is illustrated in Figure \(\PageIndex{1}\).

Figure \(\PageIndex{1}\)

Our stable climate has been enabled by fairly constant levels of atmospheric CO₂, a trace atmospheric gas, which has hovered around 280 parts per million (ppm) until the start of the industrial revolution in 1770. CO₂ is a greenhouse gas, which as anyone who has run an IR spectra knows, absorbs in the infrared. CO₂ in the atmosphere absorbs some of the infrared radiation released by the earth, allowing the earth to be warmer than in its absence. The CO₂ effectively acts as an insulating blanket. In fact, without CO₂ or other "greenhouse" gases, the earth would be completely covered by snow.

Other greenhouse gases in the atmosphere include methane and nitrous oxide. The IR spectra of these gases are shown in Figure \(\PageIndex{2}\). Students who have taken organic chemistry labs and obtained IR spectra of samples always blank the instrument to remove spectral signals from both CO₂ and H₂O.

CO2

CH4

N2O

Figure \(\PageIndex{2}\): IR spectra of some greenhouse gases. NIST (ex: https://webbook.nist.gov/cgi/cbook.c...ndex=1#IR-SPEC)

Since the start of the industrial revolution, humans have been releasing into the atmosphere ever-increasing amounts of CO₂ from the burning of fossil fuels and methane from agricultural practices and natural gas production.  CO₂ levels, as of November 2022 have reached 415 ppm, while methane has increased to 1900 part per billion (ppb) or 1.9 ppm. Increasing methane in the atmosphere contributes about 20% of the global warming effect of the more concentrated CO₂, given methane's intense IR absorbance spectra. It has a short half-life in the atmosphere (about 20 years) compared to that of CO₂ (hundreds of years). Nitrous oxide (N₂O) is also a powerful greenhouse gas, which also depletes ozone in the stratosphere. Our increased use of synthetic fertilizers and manure is the primary anthropogenic source of N₂O. Its emission is exacerbated from poorly drained farmlands.

Global Warming Potential

The global warming potential (GWP) is used to calculate the total contribution of all emitted greenhouse gases. It is expressed in units of CO₂ equivalents. It adds the contribution of other greenhouse gases like CH₄ and nitrous oxide (N₂O), each of which has unique IR absorption spectra (as shown in Figure 2 above) and atmospheric half-lives. The IPCC uses a 100-year time frame for the calculation of the GWP, which is often abbreviated as GWP100, and uses this formula:

\begin{equation}
\mathrm{CO}_2 \text { equivalent } \mathrm{kg}=\mathrm{CO}_2 \mathrm{~kg}+\left(\mathrm{CH}_4 \mathrm{~kg} \times 28\right)+\left(\mathrm{N}_2 \mathrm{O} k g \times 265\right)
\end{equation}

• CO₂ has GWP of 1 by definition since it is the reference. Its time frame in the atmosphere (100s to 1000 years) doesn't matter since it is the reference.
• CH₄ has a GWP of around 27-30 over 100 years. It reflects its higher IR absorbance but lower life-time (around 12 years).
• N₂O has a GWP of around 265-273 over a 100-year timescale. N₂O has a life-time of around 109 years.

Water is also a greenhouse gas as you can attest to on humid days and how its lack in the atmosphere in deserts leads to a large temperature drop at night. It's very different than other greenhouse gases. Its concentration varies enormously (from 40 ppm to 40000 or more) based on humidity and precipitation events, which remove it from the atmosphere. The amount of water in the atmosphere increases with increasing global temperatures, which gives rise to more intense precipitation events and also to warmer temperatures in a positive feedback loop. Its concentration in the atmosphere hence changes enormously on the time scale of hours and days, so its half-life in the atmosphere is short. In contrast, the half-life of CO₂ in the atmosphere is measured in decades to centuries.

Climate changes over the last million years

The Skeptic's Corner: Climate Change Misinformation

Climate has always changed. Our present period is no different, so there is no need for action.

Indeed, the earth has been subject to cycles of glaciation and deglaciation for hundreds of thousands of years. Luckily, we are able to determine atmospheric levels of CO₂ dating back to hundreds of thousands of years ago by measuring entrapped CO₂ in ice cores from Antarctica and Greenland. In addition, we've been able to infer the temperature over this time frame using proxies for temperature (tree rings, fossils, and more as described in section 31.2). Figure \(\PageIndex{3}\) shows how atmospheric CO₂ and temperature have varied over the last 800,000 years using ice core data.

Figure \(\PageIndex{3}\): Atmospheric CO2 concentrations (ppm, red) and temperature deviations from the past 1000 years (green) using ice core date and temperature proxies.

Several key features of the graph should be apparent:

• Both atmospheric CO₂ and temperature change (ΔT) are periodic. So yes, it is obviously true that "climate changes" as climate change skeptics argue
• Both CO₂ and ΔT change in synchrony. An obvious question might be what changes first. Does ΔT drive CO₂ changes or vice versa? More on that in a bit.
• The CO₂ levels in more modern times (right hand side of the graph) have soared in ways not seen in the last 800,000 years! This change is caused by CO₂ emissions from the burning of fossil fuels.

In those 800K years, the earth has experience cycles of glaciation/deglaciation with recurring ice ages. Figure (\PageIndex{4}\) below shows a depiction of the last ice age which peaked 21,000 years ago (left). At that time, the ice cap over New York City was about 1 mile high (right) as CO₂ was at 185 ppm!

Figure \(\PageIndex{4}\): The Laurentide glacier during the last ice age (left) and its peak height over present-day Manhattan. https://www.climate.gov/news-feature...oming-sunlight

By 5000 BCE, the glacier had retreated to more modern levels, leaving ice over the Arctic ocean, and over Greenland. CO₂ levels were then around 260 ppm.  A change of just 100 ppm in CO₂ was sufficient to lead to the melting of the Northern Hemisphere glaciers. The image above is not "Northern Hemisphere-Centric" since the great glaciers were localized in the Northern Hemisphere in the ice ages. That's because glaciers grow over land and most of the land on the planet is in the Northern Hemisphere. (Our climate studies won't include the time when one continent - Pangea- existed.) The video below shows an animation of the Northern Hemisphere ice shield as it changed with time from 19,000 BCE to now to a projected future that assumes little action to change CO₂ emissions.. Pay special attention to the graphs which show sea level changes as well.

Best estimates by Tierney et al now show that during the last ice age, the average global temperature was 6 degrees Celsius (11 F) cooler than today, which in the 20^th century is 14 C (57 F). The Arctic however was much colder (about 14 C or 25 F). The group also came up with an estimate of climate sensitivity, the increase in temperature with increasing CO₂. That value is a rise of 3.4 C (6.1 F) for a doubling in CO₂. In 1896, Arrhenius, recognizing that CO₂ was a greenhouse gas, actually calculated that doubling atmospheric CO₂ would cause a rise of 4-5 °C. No one can say we haven't known!

What the science shows

Climate, CO₂ and temperature have always changed over geological time, but our present rise in anthropogenic CO₂ in such a brief time is unprecedented and has led to CO₂ levels that far exceed those during the warmer interglacial periods when Northern Hemisphere glaciers had retreated.

The Ice Ages, CO₂ and Temperature 

The Skeptic's Corner: Climate Change Misinformation

It's not increasing CO₂ that is causing any observed increases in temperature. CO₂ is going up after temperature increases so we don't have to worry about CO₂ levels. It's just a natural process and requires no action to reduce fossil fuel use. Why reduce it if it doesn't cause global warming?

Data and models show that the global increase in temperature is driven mostly by increases in CO₂ (and not increasing temperatures driving increasing CO₂) as the predominant cause. That begs the question as to what starts the process of deglaciation. It turns out that cyclic increases in solar irradiance that increase temperatures, especially in the Northern Hemisphere, start deglaciation. A prime factor is the changes in the orbital dynamics of the earth with respect to the sun. As you know, the orientation of the earth's rotation axis remains generally fixed and pointed in the same orientation as the earth rotates around the sun. This fixed orientation leads to our annual spring, summer, fall, and winter cycles on earth. In the winter, the northern hemisphere is pointed away from the sun, leading to decreased solar irradiance per square meter in the Northern Hemisphere, causing winter there. When the earth is on the opposite side of the sun, the axis points in the same direction but tilts towards the sun, leading to summer in the northern hemisphere. However, the orbital dynamics of the earth do change in cyclic fashions over long periods of time. These long-term changes in the earth's orbital shape (eccentricity), tilt (obliquity), and wobble (precession) are called the Milankovitch cycle, and are illustrated in Figure \(\PageIndex{5}\). These cycles cause small temperature increases that start deglaciation. Click on each image below to download and view very short videos illustrating these orbital changes.  

Change in eccentricity (orbital shape) (100,000 yr cycle)	Change in obliquity (tilt) (41,000 yr cycle)	Axle precession (wobble) (26,000 yr cycle)

Figure \(\PageIndex{5}\): The Milankovitch cycle showing changes in the earth's orbital dynamics with respect to the sun. https://climate.nasa.gov/news/2948/m...arths-climate/

Based on these cycles, Milankovitch calculated that recurring ice ages should occur approximately every 41000 years. Ice ages did occur at this interval from about 3 million years ago (MYA) to 1 million years ago (MYA). About 800,000 YA they lengthened to about 100,000 years, which corresponds to the earth's eccentricity cycle. The increased duration of the cycle led to longer-lasting glaciers which moved further south in the Northern Hemisphere. One likely explanation for the increase in time between ice ages is that repeated glaciation/deglaciation eroded the bedrock in the Northern Hemisphere, converting it to regolith (rocks, soil, and dust). This allowed an increased velocity of movement of the glaciers to the south due to decreased frictional resistance, and thicker ice cap formation (more time to accrue ice), which required a longer time to melt. This also provided a positive feedback loop as the increased northern ice area would reflect more of the sun's energy back into space, cooling the planet. Punctuating these rhythmic orbital and ice age cycles are other events such as large volcanic eruptions, asteroid impacts, etc, that could produce minor to major changes in climate, and resulting mass extinctions.

Figure \(\PageIndex{6}\) shows how a combination of tilt angle, precession axis, and orbital shape at around 200 KYA (narrow rectangle across all the graphs) combined to lead to low glacial ice volume (bottom graph).

Figure \(\PageIndex{6}\): Milankovitch cycle contribution to ice volume over the past 1M years

If orbital changes (or forcing) trigger deglaciation, what is the role of increasing levels of the greenhouse gas CO₂, which clearly covary with temperature (see Fig 3)? Temperature increases derived from orbital and hence solar "forcing" seem to precede CO₂ increases for just short periods of time (perhaps 100 - 200 years). After that, CO₂ causes almost all of the global increase in temperatures during deglaciation, with CO₂ and temperature going up together. A global increase of about 0.3 C due to the Milankovitch cycle leads to greater Northern Hemisphere irradiance. This causes localized and limited melting of the Northern ice shield, leading to increases in ocean temperatures in the northern oceans. These increases slow a major ocean current (the Atlantic Meridional Overturning Circulation - AMOC) which inhibited the burial and return of cold water in tropical and southern oceans. This in turn led to a warming in the south accompanied by the release of large amounts of CO₂ stored in the oceans (see Carbon Cycle in 31.3). The release of this greenhouse gas was then responsible for most of the warming that lead to massive deglaciation. This "interhemispheric see-saw" transfer of heat from the north waters to the southern waters is key. For the far majority of the warming during glacial melting, CO₂ and temperature change synchronously.

Interpreting climate data is difficult. For example, it was found through measuring ¹⁵N/¹⁴N ratios that gases like N₂ and by extension CO₂ could rapidly diffuse through the compacting snow (firn, comprising the top 50-100 meters of the ice cap) until it became trapped in the solid ice beneath it. This would lead to the presence of "newer" CO₂ in older ice samples, and the conclusion the temperature changes preceded changes in CO₂. Corrections are made to the data to address the "apparent" time shift.

The CO₂ trapped in bubbles in the ice core samples from Antarctica reflects global CO₂ levels given atmospheric circulation but the temperatures measured from the same core samples (see Chapter 31.2) represent local (Antarctic) temperatures. Ice core samples from Greenland and ocean sediment samples from around the world are used to measure temperature at different locations over time. All of these data are required to model climate. Combined they lead us to our present interpretation of the linkage of CO₂ and temperature rise over time.

What the science shows

Increased solar irradiance on earth arising from cyclic changes in the Earth's orbit leads to short, small temperature increases in the North Hemisphere. These lead to the release of the greenhouse gas CO₂ from the oceans, which causes synchronous warming of the planet and subsequent deglaciation.

So when skeptics say that temperature increases preceded CO₂ increases, you can acknowledge they did but that the bulk of the warming is attributed to increasing CO₂ released from ocean stores which leads to synchronous temperature increases and deglaciation. Using the words of chemistry, small temperature increases from orbital forcing catalyzed the release of huge amounts of CO₂ dissolved in the ocean. In Chapter 31.3 we will explore the carbon cycle in more detail and look at how it affects CO₂ levels. 

Termination of the Ice Ages

How did the ice ages terminate? Contributions from the orbital forcing derived from the Milankovitch cycle play a part. Another factor seems to be dust derived from regolith, itself made by glacier movement as we mentioned above. How can that hypothesis be tested? By using proxies for dust, namely iron and long-chain n-alkanes (derived from plant waxes) that have been deposited in sediments. First let's look at a graph of CO₂ and temperature changes and superimpose those on iron and long-chain fatty acid levels, as shown in Figure \(\PageIndex{7}\).

Figure \(\PageIndex{7}\): Fe and n-alkane deposition compared to CO₂ and temperatures in the Southern Ocean over the last 500,000 years. Note that the x axis shows time in kYA going to the right. (so the past is towards the right).

A close examination of the two vertically aligned graphs from around 120 K to 130 KYA shows that the iron and n-alkane depositions are at a minimum at the same that CO₂ and temperature are peaking! What explains this negative correlation? It depends on the intimate connection of the biosphere with the nonbiological world (an arbitrary distinction). 

Iron and n-alkanes are circulated and delivered in dust. The long-chain alkanes, highly abundant in waxes and enriched in odd carbon number chains, were presumably derived from leaf waxes which prevent water loss from plants, especially during higher temperatures. Dust deposits were first observed in geological time in the switch from the warmer Pliocene (5.3 to 2.6 MYA) to the Pleistocene (2.6 MYA to 11.7KYA, see Fig 8 below). During the warmer Pliocene, the difference in global and atmospheric temperatures was lower, and with this smaller temperature gradient, winds that could globally transfer dust would be diminished. Also, the warmer Plicoene (5.3 to 2.6 MYA) would have more rain, which would have removed dust from the global circulation. 

As temperatures cooled in the Pleistocene (2.6 MYA to 11.7KYA), cycles of glaciation would produce more dust-containing regolith (rocks, soil, and dust), which would be dispersed through stronger global winds from higher temperature gradients and and less rain. Dust contains carbon (for example long chain fatty acids) and perhaps more importantly iron, which is needed for oceanic phytoplankton growth. Without Fe, the uptake of CO₂ by phytoplankton (primary production) would not occur, leading to increased CO₂ in the atmosphere. Stronger regional atmospheric winds would lead to increased upwelling of nutrients as well as deep ocean CO₂. The CO₂ would enter the atmosphere more readily in the absence of dust deposition of iron.

In summary:

• High CO₂ and high temperature (lower global temperature gradients, more rain) are associated with low dust, as measured with the proxies Fe and n-alkanes). Low dust leads to low deposition of Fe and n-alkanes in the ocean, which decreases phytoplankton primary production, the fixing of CO₂ into biomass), leading to increased CO₂ movement from the ocean to the atmosphere, increasing temperature. This is an example of a positive feedback loop (higher temperatures leading to higher temperatures.
• Low CO₂ and low temperature (higher global temperature gradients, stronger winds, less rain) are associated with high dust with Fe and n-alkanes deposition. This increases phytoplankton primary production and decreases CO₂ movement from the ocean to the atmosphere, in a negative feedback loop.

By the end of a glacial deposition cycle, dust, blown by stronger winds from higher temperature gradients, was increasingly deposited on the ice sheets. Along with leading to more heat absorption by the sheets, it would also decrease their reflectivity (albedo). Both effects would promote ice sheet melting. Also, a cooler planet during glacial maximum had less precipitation, which along with lower CO₂, would lead to more plant and tree death, increasing soil erosion and desertification, both effects which would have increased dust production and its deposition on ice sheets. Then when CO₂ rose to 280 ppm, plant life renewed itself, and dust levels dropped.  

Climate change from 66 million years ago to now

Antarctic ice core data are now available for the past 2 M years. Ocean sediment data can be used to go back even further in time to 66 million years ago (MYA) just before the dinosaurs died after the massive asteroid impact forming the Chicxulub crater buried underneath the Yucatán Peninsula in Mexico. A brief review of geological eras, periods and epochs is shown below in Figure \(\PageIndex{8}\)

Figure \(\PageIndex{8}\): Geological Era, Periods and Epochs

CO₂ levels and associated temperatures derived from ocean sediment cores going back to 66 MYA are shown in Figure \(\PageIndex{9}\).

Figure \(\PageIndex{9}\) CO₂ levels (red) and temperatures (blue) derived from ocean sediment cores going back to 66 MYA = 66,000 KYA . Data from Rae et al. Annual review of earth and planetary sciences, 49, 2021

Note again the parallel rise and fall of CO₂ and temperature. Eventually, they fall further in the Pliocene (5.3 to 2.6 MYA) and Pleistocene (2.6 MYA to 11.7KYA) epochs with cyclic glacier/interglacial periods we've discussed above. It wasn't until the late Miocene (10 to 6 MYA) that Northern hemisphere glaciation started and both poles of the planet had glacial sheets. 

The time frame shown in Figure 9 encompasses the Cenozoic era (65 MYA when the dinosaurs died to about now). CO₂ levels were much higher than today in the greenhouse Paleocene and Eocene eras but decreased to about 500 ppm in the Oligocene (34 MYA). An almost stepwise drop in CO₂ and temperature occurred in the Eocene to Oligocene transition (EOT), about 33 MYA. Data shows the development of large ice sheets appearing on Antarctica at this time. Before the EOT (33 MYA), Antarctica was ice-free, as shown in the recreation in Figure \(\PageIndex{10}\).

Figure \(\PageIndex{10}\): Reconstruction of the West Antarctic mid-Cretaceous temperate rainforest. Image credit: J. McKay / Alfred-Wegener-Institut / CC-BY 4.0. https://www.sci.news/othersciences/p...ing-09921.html

Proxy data for temperatures show that the transition was most likely caused by a decrease in CO₂ and some orbital forcing was probably involved. Present models still struggle to explain the EOT (33 MYA) transition, but it is clear that both CO₂ and temperature decreased. Where did the CO₂ go? Most assuredly into the oceans. 

To understand that, we have to understand a bit about the carbon cycle, which we will discuss more fully in the next chapter section. Let's briefly discuss the role of atmospheric CO₂ and its interaction with the ocean. The main gases in the atmosphere, N₂ and O₂, are found in very low concentrations in the ocean since they are nonpolar and generally unreactive. CO₂ is also a nonpolar trace gas, but in contrast, it can readily react with water to form HCO₃^- and CO₃^-2, which are found in great abundance in ocean reserves. Hence the ocean chemistry of CO₂ determines in large part the levels of atmospheric CO₂. The coupled reactions of CO₂ are shown below.

\begin{equation}
\mathrm{CO}_2(\mathrm{~g}, \mathrm{~atm}) \leftrightarrow \mathrm{CO}_2(\mathrm{aq}, \text { ocean) }
\end{equation}

\begin{equation}
\mathrm{CO}_2(\mathrm{aq} \text {, ocean })+\mathrm{H}_2 \mathrm{O}(\mathrm{I} \text {, ocean }) \leftrightarrow \mathrm{H}_3 \mathrm{O}^{+}(\mathrm{aq})+\mathrm{HCO}_3^{-}(\mathrm{aq})
\end{equation}

\begin{equation}
\mathrm{H}_2 \mathrm{O}(\mathrm{I})+\mathrm{HCO}_3^{-}(\mathrm{aq}) \leftrightarrow \mathrm{H}_3 \mathrm{O}^{+}(\mathrm{aq})+\mathrm{CO}_3{ }^{2-}(\mathrm{aq} \text {, sparingly soluble })
\end{equation}

This chemistry helps determine the pH of the ocean. Figure \(\PageIndex{11}\) shows atmospheric levels of CO₂ and ocean pH over the last 66 million years.

Figure \(\PageIndex{11}\): Atmospheric levels of CO₂ and ocean pH over the last 66 million years

Before the EOT at 34 MYA, atmospheric CO₂ levels were higher and ocean pH levels lower (around 7.7). After the EOT (33 MYA), atmospheric CO₂ is much lower and ocean pH is higher (more basic, 7.9 rising to 8.1). What happened to the CO₂ is a bit unclear.  Atmospheric CO₂ decreased by moving into the oceans but wouldn't that have lowered the pH based on the chemical equations presented above? It would have but it turns out that the ocean alkalinity is determined not just by H₃O⁺ produced by the equations above, but by the dissolved inorganic carbon ions, HCO₃^- (aq) and CO₃^2- (aq), which are conjugate bases. Increased HCO₃^- (aq) and SiO₄^-2 (aq) from weathering solid carbonates and silicates that entered the oceans would raise the pH of the oceans.  

A little review of introductory chemistry helps here.

Let's take bicarbonate, the weak conjugate base of the weak acid carbonic acid. HCO₃^- can act as both an acid and base.

Rx 1: Acts as an acid: HCO₃^- (aq) + H₂O (l) ↔ H₃O⁺(aq) + CO₃^2- (aq)

\begin{equation}
K_{a 2}=\frac{\left[\mathrm{H}_3 \mathrm{O}^{+}\right]\left[\mathrm{CO}_3^{2-}\right]}{\left[\mathrm{HCO}_3^{-}\right]}=4.7 \times 10^{-11}
\end{equation}

Rx 2: Acts as a base: HCO₃^- (aq) + H₂O (l) ↔ H₂CO₃ (aq) + OH^- (aq)

\begin{equation}
K_{b 2}=\frac{\left[\mathrm{H}_2 \mathrm{CO}_3\right]\left[\mathrm{OH}^{-}\right]}{\left[\mathrm{HCO}_3^{-}\right]}=2.2 \times 10^{-8}
\end{equation}

The equilibrium constant for the reaction of HCO₃^- as a base is much larger so bicarbonate is a stronger base than acid. 

Whatever the mechanism of the CO₂ drawdown, it led to decreasing temperatures in the EOT transition. Increased alkalinity of the ocean would also consume H₃O⁺, increasing ocean pH.

A summary of planetary temperatures across geological time is shown in Figure \(\PageIndex{12}\).

Figure \(\PageIndex{12}\): Temperature of earth over 500 million years. https://commons.wikimedia.org/wiki/F...alaeotemps.png. (Excel available).  Creative Commons Attribution-Share Alike 3.0 Unported

There are several key features to note. The last time CO₂ was as high as today (415 ppm) was about 3 million years ago. Repetitive cycles of glaciation/deglaciation are obvious in the Pleistocene (2.6 MYA to 11.7KYA).

In addition, at around 55 MYA, a spike in temperatures of about 5⁰ F occurred over about a 100K year timeframe. This was accompanied by a dramatic spike in CO₂ and a dramatic drop in ocean pH as measured by the loss of deep-sea CaCO₃ (chalk). These latter changes are visually evident in geological deep-sea sediment records as shown in Figure \(\PageIndex{13}\). This very short time frame is called the Paleocene/Eocene thermal maximum (PETM, 55.5 MYA), which shows very quick spikes (on the geological time scale) can and do occur. Approximately 1.5 petagrams (10¹⁵) of CO₂ were released annually during the PETM. Now we are releasing about 25 petagram per year. Our present rate of warming is much greater than the rate of warming during the PETM (55.5 MYA). The best candidates for the source of CO₂ release that caused the PETM are volcanoes, the oceans, and the permafrost. In addition, methane hydrates (a solid form of methane found in low- temperature high-pressure waters) might also be another factor. 

Figure \(\PageIndex{13}\): Overview for the Paleocene–Eocene Thermal Maximum (PETM, 55.5 MYA) data from deep-sea records and the terrestrial Polecat Bench
(PCB) drill core against age. Westerhold et al. Clim. Past, 14, 303–319, 2018. https://doi.org/10.5194/cp-14-303-2018. Creative Commons Attribution 3.0 License

Sediment cores were taken at various sites (1262, 1267, 1266, 1265, 1263, and 690) that are aligned from left to right according to the water depth from deep to shallow.  Note at 55.93 million years ago, at the start of the PETM, there was a sharp transition from light brown/gray which is enriched in chalk, to dark brown enriched in clay. Ocean acidification dissolved the chalk. It took over 100,000 years to recover.
 

Back to the Present

Let's return to more recent human history and anthroprogenic forcing of our climate. Figure \(\PageIndex{14}\) shows an interactive graph of atmospheric CO₂ over more recent times. Zoom into the steep rise in CO₂ starts which around 1760 with the industrial revolution.

 

Figure \(\PageIndex{14}\): Interactive graph of atmospheric CO₂ vs time over the last 1000 years. Historical CO₂ record from the Law Dome DE08, DE08-2, and DSS ice cores. Credits: D.M. Etheridge, L.P. Steele, R.L. Langenfelds, R.J. Francey and the Division of Atmospheric Research, CSIRO, Aspendale, Victoria, Australia. 2 Degrees Institute. https://www.2degreesinstitute.org/. Also, https://www.co2levels.org/

Orbital mechanics cannot explain the warming of the planet in the brief (in geological terms) times since the industrial revolution. Neither can volcanic activity, changes in solar activity, changes in land use (for example deforestation that slows down photosynthesis and CO₂ removal from the atmosphere), or even aerosols released on burning fossil fuels (which would actually decrease global temperature due to increased reflection of sunlight). Click on Figure \(\PageIndex{15}\) to see an animated explanation of which factors best explains the global temperature increase since 1880. The results are clear: It's us!

Figure \(\PageIndex{15}\): Factors contributing to global warming based on NASA data and NASA's Goddard Institute for Space Studies (GISS) climate models.

Unfortunately, other greenhouse gases have risen as well since 1975, as shown in Figure \(\PageIndex{16}\).

Figure \(\PageIndex{16}\): Rise in greenhouse gases since 1975. https://www.co2.earth/annual-ghg-index-aggi

Take special note of the zig-zag nature of the CO₂ curve. The curve dips a bit in the summer when CO₂ is actively removed by plants in the Northern hemisphere. Increasing methane now accounts for up to 20% of the warming observed. Figure \(\PageIndex{17}\) shows as interactive graph a very worrisome rise of atmospheric methane with time.

 

Figure \(\PageIndex{17}\): Interactive graph of atmospheric CH₄ vs time over the last 1000 years. 2 Degrees Institute. https://www.2degreesinstitute.org/

Present-day warming unequivocally is caused by humans burning of fossil fuels.

Past Climate Anomalies

The Skeptic's Corner: Climate Change Misinformation

In recorded human history there have been other times of climate change, so we shouldn't worry about the present time! Look at the Little Ice Ages!

Several dramatic but short-lived (in geological time) climate changes have punctuated recorded human history. Let's look at two, mostly to equip you to address climate skeptics. They also show the sensitivity of our climate to subtle changes.

The Little Ice Ages 

Actual and proxy temperature records show a mild period in Europe from around 950-1100 followed by colder weather, especially from 1450 to 1850. The latter period is called the "Little Ice Ages" although there was no significant expansion of the North Hemisphere ice shield. It was especially cold worldwide in 1816 when much of the world experienced a "year without summer". The effect in 1816 has a clear cause, the explosion of the volcano Mount Tambora in Indonesia on April 10, 1815.

But in addition to this identifiable influence in 1816, there was a cool period reported for the northern hemisphere from about 1800 to 1820 that started earlier than the Tambora eruption. Also, a low period of the sun's irradiance, called the Dalton Minimum, occurs from 1790-1860. Proxies for solar activity in the 1600s also show small solar irradiance drops, as we will discuss below. The dip in global average temperatures following the Medieval warm period, is shown in Figure \(\PageIndex{18}\).

Figure \(\PageIndex{18}\): Dip in global average temperatures following the Medieval warm period, By RCraig09 - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/inde...curid=87832845

Modern climate changes have been captured in literature and art. One example is a painting showing "Ice Fairs" on the Thames in London, shown in Figure \(\PageIndex{19}\).

Figure \(\PageIndex{19}\):https://commons.wikimedia.org/wiki/F...enell.jpgdfdfd

Many factors probably contributed to the Little Ice Ages including a drop in solar irradiance. A newer explanation has also been proposed. Marine records show that the water near Greenland and the Nordic seas were warmer, caused by a strengthening of the Atlantic Meridional Overturning Circulation (AMOC). This would have caused the loss of Arctic ice in the late 1300s and 1400s, cooling the water and diluting its salinity, since ice when it crystallized with a tetrahedral hydrogen-bonded coordination of water, excludes salt. This would have collapsed the AMOC and its transfer of heat to the northern waters, leading to rapid and prolonged cooling. An analogous strengthening of the AMOC was observed between 1960 and 1980, which was attributed to a long-duration high-pressure system over Greenland. A similar event might have occurred to kick-start the Little Ice Ages. Tree rings show evidence of higher solar irradiance before the Little Ice Ages, which may be associated with the initial strengthening of the AMOC.

The Little Ice Ages also affected China and may account in part for a crop failure in 1644, the year in which the Ming Dynasty fell. There was also an Arctic hurricane in 1588 that helped destroy the Spanish Armada. The Great Fire in London in 1666 was preceded by a very dry summer that followed an exceptionally cold winter. Food production were severely disrupted, which might have led to significant social change in Europe and elsewhere, much as the Plague in Europe shattered societal and cultural norms.

The explosion of Mount Tambora, in present-day Indonesia, in 1816 greatly exacerbated the effects of cooling. The ash and SO₂ aerosols block solar irradiance, Droughts, floods, cholera epidemics, famine, and migration from Europe to the US and from East to West arose in part from this event.  

One of the worst times to be alive: 536

Historians report that in 536 AD, parts of Europe, the Middle East, and Asia experienced 24 hours of darkness for up to 18 months.  Summer temperatures plummeted. Famines occurred for a few years after. It snowed in China in the summer. The worst effects were in the Northern Hemisphere but the effects were world-wide. It was probably the most pronounced cooling in the last 2000 years. To make matters worse, a pandemic erupted around 541 that spread from southern Asia to northern Europe. It had a huge effect on the Byzantine Empire and has been called the Justinian (bubonic) Plague after the Byzantine emperor. Crop failures, an expansion of trade, and an influx of rodents derived from the cold temperatures could have led to and also exacerbated the plague.

This second and severe example of cooling was shorter-lived in a geological time frame. Temperatures fell in the summer about 1.5-2.5⁰C. A "smoking gun" has been linked to this cooling, a volcanic explosion in Iceland. In addition, another eruption occurred in 540, which dropped the temperature another 1.5-2.5⁰C, and in 547. The combined effects of climate change and the plague led to a significant economic fall in Europe. Signs of airborne lead in the ice in 640, arising from silver mining, suggest a recovery of economic growth. You should ask yourself how the modern world with cope with such an occurrence. 

What the science shows

The Little Ice Ages and the climate changes preceding and after the Justinian plague had multiple causes, including volcanic eruptions, small changes in solar irradiance, and changes in the North Atlantic ocean currents and associated weather patterns. These short-term climate changes had disastrous effects on people's lives and the economic health of societies. Predicted future warming arising from CO₂ emitted from fossil fuel use (and other greenhouse causes) would bring far worse immediate and potentially irreversible consequences. It is incumbent on us as people who know the causes of climate change to act with due diligence and speed to avert the worst climate futures.

Solar Activity and Climate Change

The Skeptic's Corner: Climate Change Misinformation

It's not increasing CO₂ that causes any observed increases in temperature. The sun's activity is changing. It always has and always will. There's nothing we can do about it.

We have discussed how the orbital forcing of the climate kick-started each of the recurring ice ages in the Pleistocene. Some effects of the change in solar activity independent of the sun's orbit have been noted above. Specifically, we have shown that it cannot account for present warming. We present a series of graphs from the NOAA (National Oceanic and Atmospheric Administration) in the collective Figure \(\PageIndex{20}\) below to show the actual change in solar activity over recent times. Comments are shown at the bottom of each graph.

(Above) The maximal % spread from the lowest to the highest is very small. Such a small change shouldn't have such dramatic effects on climate unless it is sustained, as it was from around 1630-1700. Hence this decline in solar activity probably played some part in part of the Little Ice Ages. The regular rise and fall (spikes) are associated with the 11-year sunspot cycle activity. Note that the rise in average temperature since 1910 (shown in red) cannot be accounted for by change sin solar activity

The above graph shows that the irradiance decreased by about 0.06% (although other values have been reported as high as 0.22%) during the Maunder Minimum, which occurred in the Little Ice Ages. The average decrease in terrestrial temperatures was 1.0-2⁰C.

 

The graph above shows yearly average temperatures in the Northern Hemisphere. The dark red line shows the average change. Note that the averages are clearly lower in the Little Ice Age with the lowest values and lowest spike temperatures close to and in the Maunder Minimum.

(Above) The 11-year repeat of sunspot activity and resulting solar irradiance is clearly seen in the graphs. In 2020, a low in activity occurred, yet 2020 was the second warmest year on record since 1880.

This graph does not show the effects of climate forcing due to orbitals changes. Rather it shows that solar activity has not changed significantly for the 10000 years prior to 0 CE.

Figures \(\PageIndex{20}\): Changing in solar activity in recent geologic time.

This would be true if not for the massive amount of CO₂, approximately 1.5 trillion tons, injected into the atmosphere since the industrial revolution from the use of fossil fuels. Not all of that is still in the atmosphere, of course, but enough to raise CO₂ to levels not seen for 3 million years. Based on the relationship between CO₂ and temperature across the ice ages, science can predict when conditions might exist to initiate and propagate the next ice age. The data arising from these models, illustrated in Figure \(\PageIndex{21}\), show how much incoming solar radiation (insolation) must arrive at the earth (watts/m²) to trigger the next ice age.

Figure \(\PageIndex{21}\): Incoming solar radiation required to trigger the next ice age.

As shown in the left side of the figure, if CO₂ were 280 ppm (typical of peaks in past interglacial periods), it would take repetitive drops of insolation below the threshold of about 455 watts/m² (red line) to start glaciation. As of November 2022, we are at 415 ppm and rising. If it rises to 450 ppm, as it assuredly will in the absence of carbon capture, it would require much less insolation, since the greenhouse effect of the higher CO₂ would warm the atmosphere The right graph shows there is little chance of another ice age in the absence of large and sustained volcanic activity or asteroid impact that would lead to blocking of solar radiation.

 What science says

Changes in solar irradiance (not changes in earth's orbital dynamics) cannot account for warming since the Industrial Revolution. They have contributed to short-term (on a geological time scale) cooling during the Little Ice Ages.

Summary of Climate Change Causes and Effects Since 900 AC

Figure \(\PageIndex{22}\) shows a great summary of possible contributions to temperature change over the last 1000 years. Note again that present-day warming can only be attributed to greenhouse gases (GHG). One panel shows changes in land use. This has caused a temperature drop since 1800. That effect is caused by deforestation and other land cover changes, which leads to more reflection of incident solar radiation back into space. This effect is increased in the winter if the changed land is snow- covered. Deforestation would also decrease CO₂ capture (photosynthesis) by plants, which would raise the temperature. That component has been added to the GHG panel. 

Figure \(\PageIndex{22}\): Simulated northern hemisphere temperature changes, smoothed with an 11 year running mean, relative to the period AD 950–1250. Owens et al. J. Space Weather Space Clim. 2017, 7, https://doi.org/10.1051/swsc/2017034. Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0).

The black line in the top panel shows the observed instrumental northern hemisphere temperature variations with their associated uncertainties (Morice et al., 2012), which match the simulations well. The bottom panel shows a simulation with no changes to the radiative forcings. This quantifies the magnitude of natural internal variability in the simulations in the absence of changes in forcings. Note periodic dip but short time frame dip in temperature due to volcanic activity. Clearly, warming since the Industrial Revolution is due to emissions from the use of fossil fuels. 

Climate Justice: The Emitters and the Affected

The Skeptic's Corner: Climate Change Misinformation

Why should we make changes to reduce fossil fuel emissions when China is the biggest emitter of CO₂!

We present a series of graphs in Figure \(\PageIndex{24}\) below, taken from CO₂ Emissions - Our World in Data to show which countries have emitted the most CO₂ in the past and now. In a just world, those countries which have emitted the most should move swiftly and forcefully not only to decrease emissions but to aid other countries' transitions to clean fuels and to help them with climate change mitigation and adaptation. We don't wish to demonize the fossil fuel industry and those who work in it. The use of fossil fuels, which are high energy, high density, and cheap fuel (because of historically massive subsidies) has lifted millions if not billions out of poverty over time. We had no alternative to fossil fuels until recently. Most did not realize how significantly fossil fuel use would affect our present and future climate and the health of not only humans but the entire biosphere. (Yet there is evidence that.) We can't just stop the use of fossil fuels without inflicting great economic pain on those who can least afford it. In order to help those who are currently suffering and who will suffer most in the future, as well as to help ourselves, our children and out grandchildren, we must move away from the use of fossil fuels as soon as possible.

Above: The dip in total world emissions in 2020 was due to the COVID pandemic. Unfortunately, the rise has resumed. Note that China is now the biggest net emitter but the US and EU emissiond are dropping. India is on the rise and if they follow a similar economic path as China, which they need to lift many out of poverty, it will come with a huge cost in CO₂ emission unless they can jumpstart their conversion of clean fuels. The world needs to help.

Above: Although China is the biggest net emitter, the US and Australia are the biggest emitters per person, although that is dropping

 

The US still leads the world in the total amount of CO₂ emitted since the industrial revolution. We also have the greatest GDP. Pakistan suffered tragical flooding, exacerbated by climate change, in 2022. Up to a 1/3 of the country was under water. In a just world, the biggest emitters would aid the rest of the world.

Above: Inequality is clearly evident in this graph as the wealthiest people (high and upper-middle income) collectively contribute 86% of CO₂ emissions

Figure \(\PageIndex{24}\): CO₂ emissions by country and income since the industrial revolution. Creative Commons BY license. 

 

 What science says

The United States has emitted the most CO₂ since the beginning of the industrial revolution and the most per capita. China is not even close.

Future Projections

We know the science, and we know the consequences if we choose not to act or act in ways insufficient to meet the challenges of climate change. It is one of the most difficult challenges we have faced as a species. It requires sacrifice and united action for the common good. The benefits of our choice are mostly in the future and for future generations. 

The Intergovernmental Panel on Climate Change (IPCC), a body composed of leading climate scientists and experts, has defined several different Relative Concentration Pathways (RCPs) leading to different emissions and different climate futures. Where we end up depends on economic, social, and political choices. The IPCC initially designated four pathways, RCP 2.6, 4.5, 6, and 8.5, with higher numbers associated with higher temperatures and CO₂ levels. Each assumes a starting value and estimated emissions (which depend on technology, politics, economics, etc). RCP 8.5 assumes extra radiative forces (heat energy/(m²s)) by 2100 equal to 8.5 J/(s m²) or 8.5 watts/m². This worst-case scenario assumes business as usual with no interventions to reduce our emissions, a totally unlikely scenario given present actions (including the rapid rise of clean energy). The RCP 2.6 scenario assumes that the peak radiative forcing would be 3 watts/m² which would decline through very strong governmental and economic actions to 2.5 by 2030-2040. Table \(\PageIndex{1}\) below shows the four RCP scenarios with projected ending CO₂ equivalents (which include other greenhouse gases) and temperature increases.

Table \(\PageIndex{1}\): Four relative concentration pathways descriptions from the Intergovernmental Panel on Climate Change (IPCC) 

RCP (W/m^2)	Timeframe	CO2 atm equivalent (ppm)	Temp. increase (^oC/^oF)	Description
8.5	In 2100	1370	4.9/8.8	Rising
6.0	After 2100	850	3/5.4	Stabilizing without overshoot
4.5	After 2100	650	2.4/4.3	Stabilizing without overshoot
2.6	Decline from 3 before 2100	490	1.5/2.7	Peak and decline

Translating the projected CO₂ equivalents in the atmosphere into associated temperature increases requires a high-quality value for climate sensitivity (the rise in temperature/rise in CO₂) . Figure \(\PageIndex{25}\) shows the likely increase in temperatures for the four different scenarios.

Figure \(\PageIndex{25}\): Projected temperature rises for 4 RCP scenarios. Pörtneret al. Climate Change 2022: Impacts, Adaptation, and Vulnerability. Contribution of Working Group II to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. doi:10.1017/9781009325844.001. 

The scenarios in Figure 25 are labeled SSP#-## with the second number ## representing the RCP number. The IPCC 6th report issued in 2021 changed from using RCP scenarios to Shared Socioeconomic Pathways (SSPs) scenarios which are based on possible social and economic developments that would pose different challenges to reduce future temperature increases and hence different strategies for mitigation and adaptation. The SSP scenarios are consistent with the RCP scenarios but use a more enhanced socio-economic and political framework for their construction. The mitigation strategies are based on the RCP forcing levels. Table \(\PageIndex{2}\) below describes the SSP scenarios. They start with SSP1, which leads to a world that has adapted well and moved away from fossil fuels, to SSP5, which assumes a continued and high reliance on fossil fuels. 

SSP1	Sustainability – Taking the Green Road (Low challenges to mitigation and adaptation) The world shifts gradually, but pervasively, toward a more sustainable path, emphasizing more inclusive development that respects perceived environmental boundaries. Management of the global commons slowly improves, educational and health investments accelerate the demographic transition, and the emphasis on economic growth shifts toward a broader emphasis on human well-being. Driven by an increasing commitment to achieving development goals, inequality is reduced both across and within countries. Consumption is oriented toward low material growth and lower resource and energy intensity.
SSP2	Middle of the Road (Medium challenges to mitigation and adaptation) The world follows a path in which social, economic, and technological trends do not shift markedly from historical patterns. Development and income growth proceeds unevenly, with some countries making relatively good progress while others fall short of expectations. Global and national institutions work toward but make slow progress in achieving sustainable development goals. Environmental systems experience degradation, although there are some improvements and overall the intensity of resource and energy use declines. Global population growth is moderate and levels off in the second half of the century. Income inequality persists or improves only slowly and challenges to reducing vulnerability to societal and environmental changes remain.
SSP3	Regional Rivalry – A Rocky Road (High challenges to mitigation and adaptation) A resurgent nationalism, concerns about competitiveness and security, and regional conflicts push countries to increasingly focus on domestic or, at most, regional issues. Policies shift over time to become increasingly oriented toward national and regional security issues. Countries focus on achieving energy and food security goals within their own regions at the expense of broader-based development. Investments in education and technological development decline. Economic development is slow, consumption is material-intensive, and inequalities persist or worsen over time. Population growth is low in industrialized and high in developing countries. A low international priority for addressing environmental concerns leads to strong environmental degradation in some regions.
SSP4	Inequality – A Road Divided (Low challenges to mitigation, high challenges to adaptation) Highly unequal investments in human capital, combined with increasing disparities in economic opportunity and political power, lead to increasing inequalities and stratification both across and within countries. Over time, a gap widens between an internationally-connected society that contributes to knowledge- and capital-intensive sectors of the global economy, and a fragmented collection of lower-income, poorly educated societies that work in a labor-intensive, low-tech economy. Social cohesion degrades and conflict and unrest become increasingly common. Technology development is high in the high-tech economy and sectors. The globally connected energy sector diversifies, with investments in both carbon-intensive fuels like coal and unconventional oil, but also low-carbon energy sources. Environmental policies focus on local issues around middle and high income areas.
SSP5	Fossil-fueled Development – Taking the Highway (High challenges to mitigation, low challenges to adaptation) This world places increasing faith in competitive markets, innovation and participatory societies to produce rapid technological progress and development of human capital as the path to sustainable development. Global markets are increasingly integrated. There are also strong investments in health, education, and institutions to enhance human and social capital. At the same time, the push for economic and social development is coupled with the exploitation of abundant fossil fuel resources and the adoption of resource and energy-intensive lifestyles around the world. All these factors lead to rapid growth of the global economy, while global population peaks and declines in the 21st century. Local environmental problems like air pollution are successfully managed. There is faith in the ability to effectively manage social and ecological systems, including by geo-engineering if necessary.

Table \(\PageIndex{2}\):Summary of SSP scenarios. Riahi et al. Global Environmental Change. 42, January 2017. https://doi.org/10.1016/j.gloenvcha.2016.05.009. Creative Commons license 

The projected increases in emitted CO₂ (Gigatons/yr) and other greenhouse gases over the next 80 years for each SSP scenario are shown in Figure \(\PageIndex{26}\).  The second number in the SSP label is the RCP scenario number based on radiative forcing listed in Table 1 above.

Figure \(\PageIndex{26}\): Projected increases in greenhouse gases under different SSP (RCP) scenarios. Masson-Delmotte et al. Climate Change 2021: The Physical Science Basis. Contribution of Working Group I. to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 3−32, doi:10.1017/9781009157896.001.

Note the welcome decline in SO₂ which causes acid rain as well as aerosols. This shows that under all SSP scenarios, we are moving to clean up our air (in this case reducing SO₂ from burning sulfur-enriched coal or capturing SO₂ before it enters the atmosphere). Paradoxically and unfortunately, decreasing aerosols leads to increasing temperatures due to lower reflectance of incident solar irradiation. 

Our final figure, Figure \(\PageIndex{27}\), shows how each greenhouse gas and SO₂ are projected to change in 2081-2100, compared to 1850-1900 levels, for each of the SSP scenarios.  

Figure \(\PageIndex{26}\): Projected changes in greenhouse gas es and SO₂ in 2081-2100 compared to 1850-1900 levels for different SSP scenarios. Masson-Delmotte et al, ibid.

As all the data presented in this chapter shows, our climate fate will depend on the choices we make individually and collectively as societies. 

Key Points - Beta version from Chat.openai

1. Climate change is the long-term change in the average weather patterns on Earth.
2. The primary cause of climate change is the burning of fossil fuels, which releases large amounts of greenhouse gases, such as carbon dioxide (CO2), into the atmosphere.
3. Greenhouse gases trap heat in the atmosphere, causing the Earth's temperature to rise. This is known as the greenhouse effect.
4. The most significant contributor to climate change is CO2, which is released when fossil fuels are burned. Other significant contributors include methane, nitrous oxide, and fluorinated gases.
5. Climate change has a wide range of impacts on the Earth's systems, including rising sea levels, changes in precipitation patterns, increased frequency and intensity of extreme weather events, and disruptions to ecosystems.
6. The global temperature has already risen by 1 degree Celsius (1.8 degrees Fahrenheit) since the pre-industrial era, with most of the warming occurring in the last few decades.
7. The Intergovernmental Panel on Climate Change (IPCC) has stated that limiting global warming to 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels could significantly reduce the risks and impacts of climate change.
8. Reducing greenhouse gas emissions is essential in order to slow or stop climate change. This can be achieved through a combination of actions, such as increasing the use of renewable energy sources, improving energy efficiency, and reducing deforestation.