Our Warming Planet

Topics in Climate Dynamics

Cynthia Rosenzweig, David Rind, Andrew Lacis, Danielle Manley

• Publisher: WSPC
• Year: 2018
• ISBN:
  9789813148802
• Topic: Biological Sciences
• Subtopic: Global Warming & Climate Change
• Index: Biological Sciences

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The processes and consequences of climate change are extremely heterogeneous, encompassing many different fields of study. Dr David Rind in his career at the NASA Goddard Institute for Space Studies and as a professor at Columbia University has had the opportunity to explore many of these subjects with colleagues from these diverse disciplines. It was therefore natural for the Lectures in Climate Change series to begin with his colleagues contributing lectures on their specific areas of expertise.

This first volume, entitled Our Warming Planet: Topics in Climate Dynamics, encompasses topics such as natural and anthropogenic climate forcing, climate modeling, radiation, clouds, atmospheric dynamics/storms, hydrology, clouds, the cryosphere, paleoclimate, sea level rise, agriculture, atmospheric chemistry, and climate change education. Included with this publication are downloadable PowerPoint slides of each lecture for students and teachers around the world to be better able to understand various aspects of climate change.

The lectures on climate change processes and consequences provide snapshots of the cutting-edge work being done to understand what may well be the greatest challenge of our time, in a form suitable for classroom presentation.

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Contents:

• Understanding Climate Change:
  • Explaining Climate (Andrew Lacis)
  • Global Change in Earth's Atmosphere: Natural and Anthropogenic Factors (Judith L Lean)
  • Building a Climate Model (Gary Russell)
• Radiative Processes:
  • Atmospheric Radiation (Valdar Oinas)
  • The Role of Clouds in Climate (Anthony D Del Genio)
• Dynamical Responses:
  • How Will Storms and the Storm Track Change: Extratropical Cyclones on a Warmer Earth (Walter A Robinson and James F Booth)
  • The Relationship Between Recent Arctic Amplification and Extreme Mid-Latitude Weather (Judah Cohen)
  • The Role of Global Warming in Altering the Frequency and Intensity of Tropical and Non-Tropical Cyclones (Timothy Eichler)
• Hydrologic Responses:
  • Wisdom, Climate, and Water Resources (Robert Webb)
  • Soil Moisture in the Climate System (Randal Koster)
  • Projections of Future Drought (Jennifer Aminzade)
  • Lightning and Climate Change (Colin Price)
• Polar Responses:
  • Polar Sea Ice Coverage, Its Changes, and Its Broader Climate Impacts (Claire L Parkinson)
  • Arctic Sea Ice and Its Role in Global Change (Jiping Liu and Radley M Horton)
  • Antarctic Sea Ice and Global Warming (Douglas G Martinson)
• Paleocimate Perspective:
  • The Importance of Understanding the Last Glacial Maximum for Climate Change (Dorothy Peteet)
• Climate Change Impacts:
  • Impacts of Sea level Rise on Coastal Urban Areas (Vivien Gornitz)
  • Climate Change Challenges to Agriculture, Food Security, and Health (Cynthia Rosenzweig and Daniel Hillel)
  • Chemistry–Climate Interactions in a Changing Environment: Wildfire in the West and the US Warming Hole (Loretta J Mickley)
• Educational Perspective:
  • The Educational Global Climate Model (EdGCM) (Mark A Chandler)

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Keywords:Climate Change;Education;Climatology;Environmental Education;Earth Science;Global ChangeReview: Key Features:

• Unique format
• Subject of paramount interest
• Leading specialists presenting their fields

SECTION 1

Understanding Climate Change

CLIMATE LECTURE 1

Explaining Climate

Andrew Lacis

NASA Goddard Institute for Space Studies, New York, NY, USA

Andrew Lacis (PhD in Physics from University of Iowa, 1970) is a Senior Research Scientist at the NASA Goddard Institute for Space Studies (GISS) in New York City. He has been a member of the GISS climate modeling group since the mid-1970s. His area of expertise is development of fast and accurate radiative transfer techniques to model solar and thermal radiation with applications to the study of global climate change and the remote sensing of planetary atmospheres. He is the principal architect of the radiation modeling methodology that is used in the GISS climate GCM.

Throughout his professional career David Rind has been explaining global climate to audiences that have included students, teachers, policy-makers, scientists, and the general public. David’s great success in explaining the complexities of climate science can be inferred from the 21 PhD candidates that he advised. Their PhD dissertations, dating from 1988 to 2011, and the resulting published papers have significantly advanced our understanding of the terrestrial climate system. Of David’s 21 PhD students, all continue their top-level research in climate, with three having already been elected AGU Fellows for their outstanding research accomplishments.

Key Points and Key Components

It all begins with the Sun. The global-mean solar illumination of the Earth has been determined to be about 340 W/m² of which about 100 W/m² is reflected back to space. Hence, the Earth absorbs a global annual-mean 240 W/m² of solar energy. This amount of energy is just sufficient to support a global-mean temperature of 255 K. However, the global-mean surface temperature of the Earth is known to be about 288 K, which implies that the Planck emission from the ground surface must be about 390 W/m². It is this ‘missing energy’ circumstance that led Joseph Fourier to conclude back in 1824 that there must be an atmospheric greenhouse effect causing thermal heat energy to be radiated downward from the atmosphere in order to supply the additional heat energy needed at the ground surface. This is because in the absence of the greenhouse effect, 240 W/m² of absorbed solar energy is not sufficient to sustain a surface temperature of 288 K.

The flux difference of 150 W/m² between the 390 W/m² emitted by the ground surface and the 240 W/m² of longwave (LW) flux going out to space at the top of the atmosphere is a direct measure of the strength of the terrestrial greenhouse effect. The greenhouse action builds up the surface temperature and the surface-emitted flux to 390 W/m², and is also responsible for the ensuing reduction by 150 W/m² of the surface-emitted flux as it makes its way to space — all of that is accomplished by radiative energy processes (via sequential emission, absorption, and re-emission interactions). Detailed calculations of radiative flux attribution show explicitly that water vapor accounts for about 50% of the 150 W/m² greenhouse effect, and that LW cloud opacity accounts for 25%. Both of these radiative contributions stem from the fast feedback processes of the climate system. The remaining 25% of the terrestrial greenhouse effect comes from the radiative forcings contributed by the non-condensing greenhouse gases (GHGs, which coincidentally also act to sustain the terrestrial greenhouse effect at its present strength). Of these non-condensing GHG contributions, CO₂ is by far the strongest contributor accounting for about 20% of the 150 W/m² greenhouse effect, with the remaining 5% due to minor GHGs such as CH₄, N₂O, O₃, and CFCs (Lacis et al., 2010).

The key point is that these non-condensing GHGs behave as the principal radiative-forcing agents of the climate system because of their thermodynamic, chemical, and radiative properties. CO₂ and the minor GHGs are chemically slow-reacting with atmospheric lifetimes that range from decades to many centuries. Once introduced into the atmosphere they effectively remain there indefinitely because they do not condense or precipitate at the prevailing atmospheric temperatures while continuing to exert their radiative forcing. Since CO₂ is by far the strongest and most effective of these non-condensing radiative-forcing gases, it follows that CO₂ can be identified as the principal LW control knob that governs the global climate of Earth. The fact is that the other forms of radiative climate forcing (e.g., changes in solar irradiance, surface albedo, and aerosol forcing) are small by comparison. This makes it that much more compelling to recognize CO₂ as the principal climate control knob (Lacis et al., 2013).

Atmospheric water vapor, on the other hand, has its role as the principal fast-feedback process of the climate system — condensing and precipitating from the atmosphere in response to changes in local meteorological conditions (as constrained by the exponential temperature dependence of the Clausius–Clapeyron relation). Thus, the atmospheric distribution of water vapor (and clouds) can change rapidly in response to changing weather conditions. Radiative forcings that heat the atmosphere will cause more water vapor to evaporate, generating more LW opacity, and more radiative greenhouse effect. These changes in water vapor can produce big changes in radiative heating or cooling, but they remain limited in magnitude by how much the water vapor amount is physically able to change as it approaches its new equilibrium distribution. As a result, water vapor and clouds can only act to magnify an initial radiative perturbation, but cannot act on their own initiative to manufacture or impose a sustained warming or cooling trend on global climate, even though they may contribute more strongly to the overall atmospheric radiative structure than the radiative-forcing GHGs that actually drive and control the global temperature trend.

Cause and Effect

Global warming is basically a straightforward conservation-of-energy cause-and-effect problem in physics, and as such, not all that complicated. The basic ‘cause’ of global warming has been understood for decades, and is accurately quantified by precise measurements of atmospheric CO₂ (the Keeling curve). This reality is amply corroborated by the annual reports of fossil fuel extraction that show 10 gigatons of carbon/year (equivalent to about 10 cubic km of coal/year, which when burned, convert to nearly 5 ppm CO₂, half of which will remain in the atmosphere). The radiative effects of CO₂ and other GHGs are well understood, as is the radiative transfer modeling of atmospheric radiation. This all meshes harmoniously with the geological context made ever more clear by the precise analysis of air bubbles that have been sequestered in polar icecaps over geological time scales. Additional confirmation comes from carbon isotope analyses and direct measurements of atmospheric oxygen depletion due to the burning of fossil fuel. Still more, there is closure available from carbon cycle analyses of the ocean and biosphere uptake of about half of the CO₂ injected into the atmosphere. This leaves no room for lingering doubts that the observed increase in atmospheric CO₂ is anything but the direct result of human industrial activity. Given its radiative properties, adding CO₂ to the atmosphere restricts the natural flow of LW thermal energy to space, causing a radiative energy imbalance that requires restoration by inducing the appropriate changes in the surface and atmospheric temperature.

To be sure, it is decidedly more difficult to identify the ‘effect’ component of the global warming cause-and-effect problem with the same unambiguous clarity as the causal mechanism directly from the global temperature record. This is because the ongoing climate change consists of a steadily increasing global warming component (driven by continued injection of CO₂ from fossil fuel burning), on which there is superimposed a random-looking natural variability component (global temperature fluctuations about a reference point covering a broad range of time scales). These random-looking natural fluctuations obscure the global warming trend, but they are not random (as in random walk), such that if given enough time, they could divert the global climate arbitrarily far from its equilibrium reference point. Both real-world climate and global climate models (GCMs) must conserve energy, making arbitrarily large temperature departures from the equilibrium reference point impossible to sustain in the absence of externally applied forcing.

There are actually many different ‘climate effects’ that result from (and are thus ‘caused’ by) the steady increase in atmospheric CO₂. A more refined understanding of the Earth’s climate system requires that all of these different CO₂ change-driven effects need to be verified and documented by accurate measurements not only for purposes of numerical closure, but also for reassurance that significant climate processes have not been overlooked. Besides the widely acknowledged increase in global land surface temperature, it is equally important to monitor the changes that take place in ocean heat content and ocean temperature, the increase in atmospheric water vapor and the decrease in stratospheric temperature. The inevitable rise in sea-level concomitant with the decrease in polar ice amount needs to be monitored closely, including also the theoretically expected radiative energy imbalance between solar and thermal energy, as more solar radiation is absorbed by the Earth than is being radiated back to space in the form of LW radiation.

Radiative Forcing and Natural Variability

Accurate measurements are also needed to characterize the other radiative-forcing perturbations of the climate system, such as changes in solar irradiance, land surface albedo, and volcanic and anthropogenic aerosol loading. Not to be overlooked are the ‘virtual radiative forcings’ that arise from changes in ocean circulation that spread warm surface water from the western to the eastern Pacific as happens during El Niño events, and ocean circulation changes that promote upwelling of colder water across the eastern Pacific as occurs during La Niña events. These are examples of disequilibrium changes in the ocean surface temperature that originate from basically unforced (without any direct radiative forcing) changes in ocean circulation, which then induce feedback responses that affect the other climate variables to produce changes in climate variables that can mask the response from CO₂ radiative forcing. Long-term variability in ocean circulation also occurs on decadal time scales, and produces longer lasting regional ocean temperature variations such as the Pacific Decadal Oscillation and the Atlantic Multi-decadal Oscillation.

This unforced variability of the climate system arises because key climate system components (water vapor and clouds for the short term, atmospheric and ocean dynamics for the long term) are not configured to respond to the radiative/temperature-forcing perturbations on a sufficiently small enough incremental scale that would allow a monotonic approach to global energy balance equ...

Table of contents

• Cover
• Halftitle
• Series Editors
• Title
• Copyright
• Acknowledgements
• Contents
• Introduction
• Section 1 Understanding Climate Change
• Section 2 Radiative Processes
• Section 3 Dynamical Responses
• Section 4 Hydrologic Responses
• Section 5 Polar Responses
• Section 6 Paleocimate Perspective
• Section 7 Climate Change Impacts
• Section 8 Educational Perspective
• About the Editors
• Appendix — Supplementary Material