Toward an Ecology of Climate and Climate Change. Schwartz S. E. Priestley Lecture. Centre for Australian Weather and Climate Research (CAWCR) 5th Annual Workshop on Atmospheric Composition Observations and Modelling and the Cape Grim Annual Science Meeting. Commonwealth Scientific and Industrial Research Organisation (CSIRO) and Australian Bureau of Meteorology, Melbourne, Australia, November 16, 2011.

The ecological approach to the study of Earth's biosphere has made major advances by examining flows of energy and materials among major compartments and by identifying and quantifying the conservation laws that govern an ecosystem as a whole. This approach contrasts with one that catalogs individual species: their numbers, birth rate, development, death rate, transport, use, and release of energy and specific chemical substances, and the multiple interactions of all the individual species. An "ecological" approach to the study of Earth's climate system -- identifying the major compartments of Earth's climate system and quantifying the couplings among these compartments -- may thus likewise advance understanding of the climate system and its responses to forcings.

Important "ecological" variables of Earth's climate system are the global mean surface temperature (GMST), absorbed and emitted radiation, and the flow of energy between the upper compartment of the climate system, which is radiatively coupled to space and which is responsible for weather, and the deep ocean, the major contribution to global heat capacity. A primary objective of climate research is determination of the so-called equilibrium climate sensitivity, the normalized change in GMST that would ultimately result from a given sustained forcing. This equilibrium sensitivity serves as a metric for assessing the amount of carbon dioxide that might be added to the atmosphere consistent with a given allowable increase in global temperature. As the climate sensitivity depends strongly on changes in atmospheric composition and structure with changing temperature, much current research focuses on determining the processes controlling these elements of the climate system and representing them in increasingly complicated climate models.

An alternative, "ecological" approach examines the response of major compartments of the climate system to forcing over the industrial period. Observationally the rate of increase in ocean heat content over the past 50 years has been proportional to the increase in GMST. This proportionality leads to an expected proportionality between the increase in GMST and forcing, where the constant of proportionality is denoted the transient climate sensitivity. The transient and equilibrium sensitivities found for several published forcing data sets, which depend strongly on the forcing data set employed, are lower to well lower than the IPCC (2007) estimate for equilibrium sensitivity. The time scale for reaching the equilibrium temperature change following imposition of a forcing, about 500 years, suggests that the measure of climate sensitivity relevant to policy considerations is the lower, transient sensitivity.

This page was last updated 2011-11-13.

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