21: Natural Climate Processes
- Page ID
- 10188
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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 dominant climate process is radiation to and from the Earth-ocean-atmosphere system. Increased absorption of solar (shortwave) radiation causes the climate to warm, which is compensated by increased infrared (IR, longwave) radiation out to space. This strong negative feedback has allowed the absolute temperature at Earth’s surface to vary by only 4% over millions of years.
But small changes have indeed occurred. Recent changes are associated with human activity such as greenhouse-gas emissions and land-surface modification. Other changes are natural — influenced by astronomical and tectonic factors. These primary influences can be amplified or damped by changes in clouds, ice, vegetation, and other feedbacks.
To illustrate dominant processes, consider the following highly simplified “toy” models.
- 21.1: Radiative Balance
- This page examines Earth's radiation balance with and without an atmosphere, calculating an effective emission temperature of -18°C and detailing the greenhouse effect's role in raising surface temperatures. It outlines the dynamics of incoming solar radiation, albedo, and outgoing infrared radiation, noting that 89.9% of IR emissions are absorbed by the atmosphere. In an opaque atmosphere, surface temperatures can rise to about 30.2°C, while real-world conditions yield around 23.
- 21.2: Astronomical Influences
- This page examines the impact of solar radiation changes on Earth's climate through Milankovitch Theory, highlighting eccentricity, obliquity, and precession as key orbital factors affecting insolation and climate events like ice ages. It describes the implications of obliquity and precession variations over long and short timescales.
- 21.3: Tectonic Influences
- This page addresses the dynamics of tectonic plate movement and its consequences, including the formation and disintegration of supercontinents like Pangea. It explores how these shifts affect climate and weather patterns, including monsoons and ocean currents. Additionally, it examines the climatic impacts of volcanic eruptions, detailing both short-term cooling effects from ash and sulfur dioxide and long-term warming from greenhouse gases.
- 21.4: Feedbacks
- This page covers feedback mechanisms in physical and climate systems, including linear vs. nonlinear responses. It explains how feedback alters system responses, with positive feedback amplifying and negative feedback stabilizing. Key concepts include ice-albedo feedback, infrared and water vapor effects, and the complex roles of clouds, aerosols, and greenhouse gases.
- 21.10: Homework Exercises
- This page provides comprehensive exercises and activities for students to enhance their understanding of climate science and Earth's orbital mechanics. It includes topics such as solar irradiance, climate feedback processes, and energy balance analyses. Students will explore Earth's climate system, orbital parameters, and real-world applications like the Daisyworld model and climate change implications.
- 21.5: Gaia Hypothesis and Daisyworld
- This page discusses James Lovelock's Gaia hypothesis, which proposes that life actively regulates Earth's climate for stability. It introduces the daisyworld model, illustrating how light and dark daisies affect global temperature: dark daisies retain heat in cold, while light daisies reflect it when warm. Through simulations of solar intensity and daisy populations, the model shows how these relationships can maintain ecological homeostasis, with temperature stability between 0.94 and 1.
- 21.6: GCMS
- This page discusses Global Climate Models (GCMs), which are crucial for long-term climate forecasting. They operate using grid points or spectral methods and can simulate future climates, although they struggle with coarse grid spacings that mask smaller phenomena.
- 21.7: Present Climate
- This page discusses climate as the long-term average of weather over 30 years, introducing the Köppen Climate Classification system by Wladimir Köppen. It categorizes climates based on temperature and precipitation patterns using two- or three-letter codes relating to regional vegetation. The classification has evolved with modern data, supported by accompanying tables and figures.
- 21.8: Natural Oscillations
- This page covers the concept of "normal climate" and natural climate oscillations, explaining their impact on global weather patterns via indices such as ENSO and PDO. It details statistical approaches like Principal Component Analysis (PCA) for analyzing temperature anomalies and deriving Principal Components that summarize variance in climate data.
- 21.9: Review
- This page explains climate as the long-term average of weather, detailing both external and internal influencing factors. It covers the greenhouse effect, its inefficiencies, and the role of greenhouse gases. It discusses feedback mechanisms that can stabilize or amplify changes and mentions short-term variations like El Niño. Analytical tools such as Hovmöller diagrams are presented, alongside ethical considerations in scientific research to prevent misconduct that could skew findings.