science activities

focus 1 - climate forcings and modeling
rationale

A climate forcing is defined as an imposed radiative perturbation of the Earth’s energy balance, either natural or anthropogenic. The sensitivity of the climate system to an imposed forcing is dependent not only on the magnitude and character of the climate forcing but also the feedbacks within the climate system that amplify or diminish the responses. Some climate change agents can be considered as a climate forcing or as a climate feedback depending on the time scale of interest. The concentration of atmospheric carbon dioxide is an example of a climate forcing and a climate feedback. Over the last few hundred years, anthropogenic increases in this greenhouse gas have imposed a significant climate forcing on the system. Over glacial-interglacial cycles, carbon dioxide has varied naturally as a feedback of the climate system to orbital solar forcings.

Direct measurements of climate forcings from ground-based and satellite observing systems are available for the last several decades to half century. These measurements allow us to understand and calibrate indirect measures of past climate forcings from proxy evidence as recorded in historical records, ice cores, tree rings, and lake and ocean sediment records. The challenge of this focus is to produce improved, extended, and consistent time series of climate forcings and feedbacks, both natural and human-made, including solar insolation and irradiance intensity (or luminosity), volcanic activity, land-cover change, and greenhouse gas and aerosol concentrations. Accurate reconstructions of the climate forcings then allow climate system models to be used to quantify the sensitivity of the climate system, spatially and temporally, and to understand the natural variability of the climate system. It allows us to put the present, past, and projected future climate changes in context. Emphasis lies on the last 2000 years at annual, the Holocene at annual to centennial, and the Pleistocene at glacial-interglacial to sub-millennial timescales.


goals

1. Improved understanding of solar irradiance variations and correlation with sunspot number, and cosmogenic signatures in ice cores and tree rings; disentangle solar from non-solar influences on these proxies; extend low-frequency record back through the entire Holocene; more detailed and spatially distributed records of cosmogenic isotopes, and associated modeling of the different mechanisms able to affect their concentration in ice and marine sediments.

2. Correlation of more ice core records to establish dates, latitude, and magnitude of explosive volcanic eruptions; development of new tracers, such as sulfur and oxygen isotopes in sulfate of ice cores, to identify stratospheric eruptions; estimation of size distribution of volcanic eruptions; extend record through the entire Holocene; development of new tracers to constrain the radiative impact of volcanic events recorded in ice.

3. Better records and understanding of regional changes in land use and land cover.

4. Better understanding of dust loading at a variety of sites, high and low latitude, continental and oceanic to better constrain temporal and spatial character over glacial-interglacial cycles

5. Better estimates of the phasing between insolation, greenhouse gas concentrations and climate-environment responses during climate transitions; development of coupled carbon-climate models in the frame of glacial-interglacial changes, to quantitatively assess the causes of greenhouse gases/climate coupling; improved record of nitric oxide variations.

6. Improved reconstructions of past changes in sea ice cover for a better quantification of the albedo of the high-latitude oceans.



PLEASE NOTE: This is draft text pending publication of PAGES Science Plan and Implementation Strategy.