14.2: Investigation - IPCC AR6, the Physical Science Basis of Climate Change
- Page ID
- 53322
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The Intergovernmental Panel on Climate Change (IPCC) is a United Nations organization comprising scientists and other professionals from various countries. This group continually synthesizes research papers published in the scientific literature to make updated assessments and predictions on Earth's climate, and periodically publishes its results as Assessment Reports. The latest in this series is Assessment Report 6 (AR6), published in 2021. Like previous assessment reports, IPCC AR6 is a comprehensive report aimed at various audiences, including specialists, policymakers, and the general public. IPCC AR6 - The Physical Science Basis Technical Summary is notably suitable in technicality and conciseness for the PHY SCI 101 class.
In the Technical Summary, two sections outline the roles of the earth system in climate change. First, the section "Selected Updates and/or New Results since AR5" provides a summary of the key updates from AR5. It reaffirms the conclusions in AR4 and AR5 that "warming of the climate system is unequivocal" and that "human influence on the climate system is clear". It states that the increase of the leading greenhouse gases of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in the atmosphere was due to human activities. This section updated the warming to date; it states that "changes in observational understanding alone between AR5 and AR6 leads to an increase of about 0.1°C in the estimated warming since 1850–1900. For the decade 2011–2020, the increase in global surface temperature since 1850–1900 is assessed to be 1.09 [0.95 to 1.20] °C."
Second, the section "The Carbon Cycle" provides an explanation of the sources and sinks of CO2 in the Earth system and an estimation of the increased amount of CO2 in Earth's atmosphere at the present time and in the future. Specifically, it points out that the sources of CO2 increase are combustion of fossil fuels and land-use change for the period 1750–2019. These sources resulted in the release of 700 ± 75 Pg (1 Pg = 1012 kg) of carbon to the atmosphere, of which about 41% ± 11% remains in the atmosphere today. Of the total anthropogenic CO2 emissions, the combustion of fossil fuels was responsible for about 64% ± 15%. The remainder resulted from land-use change. During the last decade (2010–2019), average annual anthropogenic CO2 emissions reached the highest levels in human history at 10.9 ± 0.9 Pg/yr. Of these emissions, 46% accumulated in the atmosphere, 23% was taken up by the ocean, and 31% was removed by terrestrial ecosystems.
The impact of a greenhouse gas on per molecule basis is quantified by the parameter of global warming potential (GWP), the relative capacity for trapping heat in Earth's atmosphere. Complete the table below for the GWPs for the three leading greenhouse gases:
| Greenhouse Gas | Global Warming Potential (CO2 eq) |
|---|---|
| Carbon Dioxide | 1 |
| Methane | |
| Nitrous Oxide |
Consider the known temperatures and CO2 concentrations at several landmark prehistoric or recent times, as well as the temperature for the hypothetical condition if Earth's atmosphere had no greenhouse gases. Complete the following table to show how temperatures and CO2 concentrations mutually correlate in Earth's history. The data needed to complete the table can be obtained from Wikipedia or other sources.
| Time or Condition | CO2 Concentration (ppm) | Temperature (°C) |
|---|---|---|
| If Earth's atmosphere had no greenhouse gases | 0 | |
| Last Glacial Maximum | ||
| 1750, before Industrial Revolution | ||
| 1950 | ||
| 2023 (IPCC AR6) |