Fundamentals of Climate Change is a class for upper-level undergraduates and graduate students at University of Washington.

Introduction

“Sure has been hot lately! But climate has always changed, right?…”

Lessons on global warming often start with observations of how much the planet has warmed in recent years. After demonstrating the substantial rise in temperature since pre-Industrial times, the question of what has caused this warming is then addressed (spoiler alert: the answer is unequivocally fossil fuels). Scientists, however, often consider quite the opposite line of argument, starting with the large changes in atmospheric composition. Let’s begin our lessons with that point.

Industry Has Changed Atmospheric Composition

The atmosphere above us is remarkably thin, less in relative thickness to the Earth as the seams on a basketball. 90% of the mass of the atmosphere is within just 16 km of sea level. The equator-to-pole distance is hundreds of times larger than the atmospheric depth: 10,000 km, nearly exactly, as this was the original definition of the meter. Although it seems infinite when we look upward, the atmosphere is rather finite. This is part of the reason that industrial activity has been able to change atmospheric composition.

Another reason is that the critical constituents in the atmosphere that affect temperature are rather scarce. Carbon dioxide (CO₂), the critical lever on climate that is also released from fossil fuel burning, is less than half a part per thousand. We’ve been measuring CO₂ accurately since the 1950s, and since that time, levels have risen from 315 ppm to 420 ppm. Fossil fuel and land use emissions over that time have been more than enough to explain the atmospheric rise. This is because some of the industrial-caused emissions have been taken up by the ocean (where it causes ocean acidification) and by land ecosystems.

Global average carbon dioxide concentration from NOAA.

Heat-trapping gases, well… trap heat

Heat-trapping gases (also known as greenhouse gases) like CO₂ cause the Earth to be a lot warmer than it would be otherwise. The natural heat-trapping effect of carbon dioxide, water vapor and other gases raise the temperature of the Earth by over 30^oC. We’d be on a frozen block of ice if it wasn’t for this so-called greenhouse effect. But there can be too much of a good thing. The additional heat trapping from rises in CO₂ amount now to over 1 petawatt (10¹⁵ watts), which is over 300 times the electricity usage on Earth.

It’s Getting Hot

It’s not surprising when so much extra heat is being trapped that the planet would warm. Indeed, temperature records (along with all sorts of other complementary data) show that the Earth has warmed a lot. It’s about 1.3^oC since pre-Industrial times, which much of that warming happening since the late 1970s. Warming has happened nearly everywhere on the planet, more over land than ocean, and more in the Arctic than anywhere else. Along with the increase in global average temperature, extreme heat events are on the rise, ice is melting, sea level is rising, and both floods and droughts are increasing.

Whodunnit?

The warming is consistent with the heating from industry-induced changes. But exactly how much of the observed temperature increase is due to industry, and how much is due to natural factors? The best scientific estimate is 100% industry, 0% natural. There’s no evidence that natural factors alone would have caused any global warming recently, much less the greater than 1^o C temperature rise seen so far.

Over the next few chapters, we’ll establish how heat-trapping gases like carbon dioxide and methane affect the energy balance of the planet, and other factors that contribute. There are many independent lines of evidence that support the conclusion that warming is caused by industrial emissions. On a more regional scale, year-to-year climate variability cause a scrambling of the global signal. Sloshing of heat within the atmosphere and ocean are crucial to this behavior, and understanding the ways in which geophysical fluids move provide the basis for understanding climate variability as well.

Water is critical to climate as well as life on our blue planet. We’ll study why humidity rises in warmer climate, and how this amplifies both global warming as a whole and extremes of the hydrologic cycle. Precipitation patterns like monsoons and storm tracks are affected by both the amount of water vapor in the air and atmospheric circulation. Our survey of air motions will float through the Hadley Circulation, soar into the Intertropical Convergence Zone, and spiral through cyclones.

In order to strengthen our understanding of the fundamentals, most lessons will start with why climate features exist in the first place. Then we focus on changes with global warming, both in terms of what has occurred so far and what’s projected for the future. Quantifying the certainty with which different conclusions can be made is a primary objective of this book. A deeper appreciation of the fundamentals of climate change can help you conceptualize uncertainty as something deeper than just a probability distribution. You’ll uncover the interrelations among different phenomena, and a more holistic viewpoint of our interconnected planet.