1: Climate Change
- Page ID
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)V. RAMANATHAN UC San Diego, Scripps Institution of Oceanography
- Explain the basic concepts of climate change science. You will learn how some atmospheric gases emitted by human activities spread around the planet like a blanket and how that blanket traps infrared radiation (heat radiation) and warms the planet. Such gases are popularly called greenhouse gases. A basic knowledge of climate science will help motivate you to solve the problem of increased greenhouse gases. You will be able to explain the underlying scientific principles of climate change to others, including skeptics.
- Discuss the anthropogenic drivers of climate change. Next you will learn how our various activities—driving, flying, cooking, heating and cooling homes, and producing food—contribute to climate change. Because these drivers are related to human activities, we call them anthropogenic drivers of climate change (anthropogenic is the scientific term for “human-caused”).
- Explain how and why the climate is changing. By this point, you will know how the greenhouse gases emitted by human activities are expected to change the climate, based on physical principles. The third learning objective is to understand how the climate is changing now and how our observations of the weather are matching predictions from climate models.
- Describe the likely climate changes and their projected impacts. The fourth objective is to use the knowledge you have gained thus far to describe the potential impacts of the warming on aspects of climate that affect us all, including heat extremes, droughts, floods, sea level rise, and melting sea ice and glaciers. It is having huge impacts on almost everything we know. Climate change is causing new weather extremes such as floods, heat waves, and droughts, with negative effects on public health. It is better termed as climate disruption. We will track down the various impacts we are already experiencing today and project the impacts that are likely to occur in the future if we continue on our current path of unsustainable greenhouse gas emissions.
Overview
The climate system is dynamic and has undergone major changes in the history of the planet. Over the last 2 million years, the Earth’s climate has cycled between cool glacial periods and warm interglacial periods. These cycles have occurred about every 100,000 years over at least the past 800,000 years. Beginning 11,700 years ago, the Earth transitioned to the current interglacial warm epoch called the Holocene. Before the nineteenth century, climate change on the planet was mainly a naturally occurring phenomenon caused by changes in the Earth’s orbit around the sun, changes in the amount of solar radiation reaching the Earth, volcanic activity, and natural patterns of heat exchange between the land, the ocean, and the atmosphere.
Since the dawn of the industrial era, a new global causal factor has been added to this list: humans. We emit carbon dioxide and other pollutant gases when we burn fossil fuels and do many other things, such as refrigerate our food and fertilize our crops. These pollutants have drastically altered the heat-trapping properties of the atmosphere. In the case of carbon dioxide, the changes are irreversible on time scales of thousands of years or more. These pollutant gases now cover the Earth like a blanket, trapping infrared heat and warming the planet. The climate has already warmed by 1°C since the preindustrial era and in another 15 years (from 2018) will reach levels not seen in the past 130,000 years. Climate scientists have concluded that if the current rate of emissions continues, the planet will warm to levels not observed in the last 25 million years or more. Not only is the amount of the warming unprecedented, but the rate of change is also orders of magnitude larger than that of past natural variations.
How do we know this is true? Climate change science is intensely data driven and has undergone the traditional scrutiny and rigor of scientific methods. It has taken thousands of peer-reviewed studies over more than 100 years and large quantities of data collected from ships, surface stations, aircraft, and satellites to arrive at the conclusions described in this chapter. The findings reported here are based on analyses of literally trillions of bytes of data by thousands of scientists from around the world as reported in thousands of peer-reviewed publications. These studies have been reviewed by science academies in the United States and around the world since the 1970s, culminating in the formation of the Intergovernmental Panel on Climate Change (IPCC) by the United Nations in 1989. Hundreds to thousands of scientists contribute to the IPCC’s periodic reports that assess, evaluate, and update the science and the data. References to some of these reports are provided at the end of this chapter.
The most important messages in this chapter are that (1) anthropogenic emissions are causing climate change at a magnitude and rate that are unprecedented over at least the past million years, and (2) this human-caused climate change is likely to have severe impacts on both the natural environment and human society. Finally, it is particularly important to recognize that we still have time to act to reduce human-caused climate change and moderate or avoid the most serious impacts—if we start acting now (2019). The purpose of this book is to empower you and give you the tools you will need to act as “climate warriors” innovating and implementing climate solutions.
This chapter will also help you address questions that people you know, including climate change skeptics, might ask you. For example, how do you know the climate is changing? Even if it is changing, how do you know the change is caused by human activities? And whom do you believe?
Your answer to the last question should be simple: we do not have to believe anyone. We have the data. Thousands of scientists have analyzed and interpreted observed data from peer-reviewed studies, so these are facts, not beliefs. The real issue we want to address is the following: if we continue along the current path of unsustainable pollution, what does the future hold for us? How will the planet look a few decades from now? And what’s in store by the end of the century? The projections made by various scientific institutions are summarized in this chapter.
Hopefully these scientifically projected scenarios will give you the reasons, as well as the motivation, to solve the problem in a timely manner. As you already know, this book is about solving the climate change problem. A hopeful message comes out of the findings summarized in this chapter: there is still time to solve the problem of climate change and stabilize the climate below dangerous levels of warming.
The Intergovernmental Panel on Climate Change (IPCC) is the most prominent international scientific body for assessing climate change. It was formed in 1988 by the World Meteorological Organization (WMO) and the United Nations Environment Programme (UNEP). There are currently 195 member countries in the IPCC, and membership is open to all countries in the WMO and UN. The IPCC is responsible for reviewing and evaluating scientific, technical, and socioeconomic information related to climate change. While the IPCC neither conducts research nor monitors any climate change data directly, it provides policymakers with the most comprehensive picture of the scientific consensus.
Globally averaged greenhouse gas concentrations
Increase in atmospheric concentration of carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) with time. Reproduced from IPCC
The information assessed by the IPCC is synthesized into a major assessment report (AR) every 5 to 7 years. There are currently five multivolume assessment reports, and the latest one, AR5, was finalized in 2014. Each AR has three volumes, each of which is led by a working group. Working Group I (WGI) consists of 258 experts who assess the science behind climate change and how humans are causing it. With 302 experts, Working Group II (WGII) evaluates the impacts of climate change and how living things, such as humans, animals, and plants, can adapt. Working Group III (WGIII) has 271 experts and focuses on mitigating climate change—that is, slowing it down and preventing its worst possible effects.
AR5 has more than 830 lead authors across the three working groups from over 80 different countries. The reports submitted for any AR undergo a rigorous, multistage review process. The IPCC is currently working on AR6, and the contributions from the three working groups will be finalized by 2021. Source: https://www.ipcc.ch/organization/organization.shtml