Science Behind Climate Change
Climate is what happens over two or three decades, whereas the weather is what is happening over two or three days, at most. Some would say hours to a day (after all, doesn’t the weather change, sometimes dramatically, over the day?).
There are many reasons climate can change. Some changes are due to processes that last many years, even many millennia (think ice ages). Climate is a large-scale phenomenon, even if it isn’t the same all around the globe, and it is changed by large-scale events. These include plate tectonics and volcanism, shifts in ocean currents, and changes in various astronomical cycles (variations in the Earth’s orbit around the Sun as it can vary in “eccentricity,” which is how ovoid the orbit is, the axial tilt of the Earth and the wobble of its axis).
There are cycles that are tens of thousands of years. There is an 11-year cycle of the Sun’s magnetic field that can change its power output.
Now the climate is changing so quickly that we can speak of major, large-scale, long-term changes in the climate that are occurring over a few decades rather than centuries or millennia. This is because we humans are altering the climate in a massive fashion, and we are doing it all too well.
What Is the current climate change and what drives it?
Brief History: this is no surprise
The potential for gases to act by absorbing the energy of light and then emitting it again as heat has been known for almost 200 years, since not long after it was first discovered that air consists of gases.
Joseph Fourier in France described the basic science of gases interacting with radiant heat in 1824. In 1859 John Tyndall in Ireland, after just a month of experiments on CO2, recognized the role of atmospheric gases in trapping heat and then further refined his observations. The Swedish scientist, Svante Arrhenius, quantified the effect on global temperature in 1896.
The science advisor to President Jimmy Carter, Frank Press, predicted the global warming we have experienced over the next four decades. A memo (quoted in The Guardian 6/14/22, “The 1977 White House climate memo that should have changed the world”) warned the president that burning fossil fuels could lead to “catastrophic climate change.”
The oil companies knew all this in the 1970s and 1980s and even predicted the rise in temperature, tracking the increase in atmospheric CO2 accurately. As a 2023 article in the journal Science documents, Exxon knew exactly what was going on and chose to ignore it.
And they were right! The average global temperature has been increasing just as predicted.
Temperatures in the Contiguous 48 States, 1901–2020 From EPA.gov (https://www.epa.gov/climate-indicators/climate-change-indicators-us-and-global-temperature)
Temperatures Worldwide, 1901–2020
Here is a link to a great animation from NASA that shows 140 years (1880 to 2021) of global temperature changes: https://svs.gsfc.nasa.gov/4964
2023 was the hottest year on record and 2024 is on track to beat it.
Over 99.9% of peer reviewed scientific articles conclude that human-caused climate change is real.
The science is in. There is no doubt the Earth is warming, and burning fossil fuels is the primary reason.
Climate change mechanism: atmospheric greenhouse gas (GHG)
We start our understanding of climate change with the mechanisms of global warming. Many of us prefer the term “climate change” rather than “global warming" because while the increase in mean global temperature initiates the cascading problems of climate change, it is the complex effects on the climate and Earth systems and our ability to sustain ourselves that concern us the most. The term “global warming” is too restrictive and diverts attention to just the temperature, preventing people from having a full appreciation of what is really happening.
Of course, climate change is a bit of a neutral term. It could be good or bad! Some prefer climate crisis do capture the urgency of the situation.
But indeed, climate change starts with global warming, and that starts with sunlight.
Higher energy ultraviolet (UV) and blue light from the Sun are only partially absorbed by gases like ozone in the upper atmosphere (think high energy light that bullies its way through), so this light reaches the lower atmosphere and ground, where:
Some of the high energy sunlight is reflected by lighter colored material (“albedo”) such as clouds, snow, ice, and appropriately painted surfaces like white roofs, without adding to surface warming.
Some of the light is absorbed by darker materials, including bodies of water, soil, dark roofs and tarmac, exciting molecules, heating the material up.
The heated material (soil, water, roofs, tarmac, etc.) emits longer wavelength light (e.g., infrared) that now radiates up into the atmosphere.
The longer wavelengths that were reflected back up from the Earth’s surface are now the right wavelengths and frequencies to interact with GHG in the atmosphere. These GHG include carbon dioxide (CO2), methane (CH4), nitrous oxides (NOx, where the x can be different numbers for different oxides), water vapor, and hydrofluorocarbon gasses. The long wavelength light energizes the GHG molecules. The atoms bonded together in these GHG vibrate faster, almost as if the atoms were linked by springs, in effect heating them up.
The GHG then radiate this radiant heat energy both to space and back down into the lower atmosphere, and so the surface of the planet, heating it up.
Some heat is lost, some retained; an equilibrium. The more GHG, the more heat is retained, the hotter we are. A new equilibrium.
The term “greenhouse effect” is a rough analogy. A greenhouse lets sunlight in and then the glass traps the warmed air. The Yale Communication Project likes to use the analogy of GHG acting like a blanket trapping air your body warmed up on a cold night.
Both of these analogies (greenhouse and blanket) are not strictly correct; GHG radiate energy that they absorbed, they aren’t passively trapping heated air.
Still, these analogies have the advantage of being simple to understand and do capture the heart of the matter: heat isn’t dissipated into space as it otherwise would be if the level of GHG was lower, so the Earth heats up!
What are the GHG and CO2e?
Nitrous oxide (N2O), methane (CH4) and hydrofluorocarbons (HFC; used in refrigerants) are more powerful GHG than CO2, but CO2 is much more abundant and lasts longer in the atmosphere (centuries) so builds up. That is why CO2 is the standard used, and the other GHG are converted to CO2 equivalents (CO2e) in most reports.
Water vapor in the atmosphere is also a more powerful greenhouse gas than CO2, but it is part of the natural cycle, a necessary component of the atmosphere that is essential to us, not part of anthropogenic (human made) climate change, and not easy, or necessarily desirable, to change globally. Water vapor is also relatively constant, though it may increase locally or regionally as warmer air evaporates more water and the warmer air can hold more water. That doesn’t mean it need not be considered, say in climate models, as it may play a role in outcomes and feedback loops, just that we aren’t going to alter it directly and it isn’t due to industrial processes or burning fossil fuels. It is not a cause of the current climate crisis!
CO2 =1
CH4 = 25
N2O = 298.
HFC = Many HFC are hundreds or thousands of CO2e. There are many types of HFCs and their CO2e vary, as high as 22,800 for sulphur hexafluoride (SF6). These are much less common GHG but a major problem still.
CO2 in the atmosphere is essential to life. CO2 sustains the food chain through photosynthesis. If you do the math, you will find that without natural GHG the average temperature on Earth would be about 0 degrees Fahrenheit (F) or -18 degrees Celsius (C), an unacceptable equilibrium temperature for life as we know it!
But that doesn’t alter the fact that our civilization developed under circumstances of relatively stable CO2 concentrations in the atmosphere, and so a particular climate and sea level, so changes can have devastating effects on the ability of civilization to continue to thrive or even survive.
The warming is not spread evenly around the globe. There are factors, such as albedo (reflective surfaces like ice and clouds), ocean currents, and regional large bodies of water that can absorb and hold more heat, the effect of trees releasing water in photosynthesis, and geologic features, that can alter the local effects of climate change. Most of the heat is absorbed by the oceans. Some areas may even be cooler, another reason not to favor the term “global warming.”
Regarding increased temperature, globally the most impacted area is the northern hemisphere, the Arctic in particular. In the United States, there are some areas in the south that are less involved.
Rate of Temperature Change in the United States, 1901–2020
The problem
The average temperature has risen globally about 1 degree C 1.8 F, or slightly more, now more like 1.1 C, since preindustrial times, often considered from 1880 (when the temperature data were first regularly collected, though the Industrial Revolution started a century earlier).
Electricity, the internal combustion engine and petroleum were game changers.
Half of the increase in temperature has occurred since 1970. The last 8 years were the hottest 8 on record; 2022 was the 5th hottest, 2016 the hottest recorded. As noted above, 2023 was the hottest year on record and 2024 is on track to beat it.
That temperature rise doesn’t sound like much, but it is an average, and it is enough to destabilize our climate and result in cascading effects that can bring down our civilization and make large areas of the globe uninhabitable for humans if it gets much worse.
And if we don’t do something, it will get much worse.
The fact is we need to get this under control as quickly as we can. We are already in trouble.
Many of the books in the bibliography will enlighten you if you want the gory details of the predicted impacts that will happen if we don’t deal with this. Perhaps that will inspire you to act with a sense of urgency.
Which scenario happens depends on us.
Since we generally hope to keep it to an increased average temperature of 1.5 C or less, you can start with this if you like; even if we keep to a target of 1.5 C rise over preindustrial temperatures, the problems can get out of hand.
Let’s agree it is urgent and we have to act.
In order to better grasp what is already happening now, and what we can do about it, we want to understand the processes involved.
It isn’t just about feeling a bit warmer sometimes, it’s the effects it has on the ecosystem and our lives. Read more about why we care here.
Additional Resources
Websites:
https://www.climate.gov: section on climate change: global temperature. A useful website with much information, with maps and data and a section on resilience.
IPCC reports: https://www.ipcc.ch/reports/: a treasure trove of well-reviewed information on the basic science but even the summaries are long.
https://www.noaa.gov: (The National Oceanic and Atmospheric Administration) is a great source for information and updates.
The EPA on climate change science: https://www.epa.gov/climatechange-science and https://www.epa.gov/ghgemissions/overview-greenhouse-gases
UC San Diego and the Scripps Institute of Oceanography https://keelingcurve.ucsd.edu.; https://scrippsco2.ucsd.edu for updated CO2 data
Climate Reanalyzer https://climatereanalyzer.org from the Climate Change Institute at the University of Maine is a website that has weather and climate data wonderfully displayed.
Books:
Most books on climate change have introductory chapters; recent books with relevant chapters:
“From Knowledge to Power. John Power. Ooligan Press, 2021. Chapters 1 and 2.
The Carbon Almanac, it’s not too late. Forward by Seth Godin (This is a large collaboration by the Carbon Almanac Network). Portfolio Penguin, 2022. Section “Climate Change for Rookies” pages 20-90. On pages 46-47 there is a reproduction of memos from Exon (as the oil company was then called) showing that the giant oil company knew exactly what was going on in 1982!
The Thinking Person’s Guide to Climate Change. Robert Henson. AMS books, 2019. This is from the American Meteorological Society. Chapters 2 and 3 cover the science and basic processes.
Global Climate Change and Human Health. Jay Lemery, Kim Knowlton, Cecilia Sorensen, 2021. Chapter 1 for scientific background of climate change.
Saving Us. Katherine Hayhoe. One Signal Publishers, 2021. An excellent book by the chief scientist for The Nature Conservancy who has a track record of public engagement.