Communicating global climate change using simple indices: an update

Abstract

Previous studies have shown that there are several indices of global-scale temperature variations, in addition to global-mean surface air temperature, that are useful for distinguishing natural internal climate variations from anthropogenic climate change.Appropriately defined, such indices have the ability to capture spatio-temporal information in a similar manner to optimal fingerprints of climate change. These indices include the contrast between the average temperatures over land and over oceans, the meridional temperature gradient, the temperature contrast between the Northern and Southern Hemisphere and the magnitude of the annual cycle of average temperatures over land. They contain information independent of the global-mean temperature for internal climate variations at decadal time scales and represent different aspects of the climate system, yet they show common responses to anthropogenic climate change. In addition, the ratio of average temperature changes over land to those over the oceans should be nearly constant for transient climate change. Hence, supplementing analysis of global-mean surface temperature with analyses of these indices can strengthen results of attribution studies of causes of observed climate variations.In this study, we extend the previous work by including the last ten years of observational data and the CMIP3 climate model simulations analysed for the IPCC AR4. We show that observed changes in these indices over the last ten years provide increased evidence of an anthropogenic influence on climate. We also show the usefulness of these indices for evaluating the performance of climate models in simulating large-scale variability of surface temperature.

Using palaeo-climate comparisons to constrain future projections in CMIP5

“…Braconnot et al, , 2012Laîné et al, 2009), while, in a symmetric manner, predictions for future climate show a stronger warming over land than over the oceans (e.g. Sutton et al, 2007;Drost et al, 2012). The ratio between cooling over non-glaciated land and cooling over the ocean for the LGM tropics was ∼ 1.3 in the PMIP1 computed sea surface temperature (SST) simulations (Pinot et al, 1999), a result close to the ratio of ∼ 1.5 found in both the PMIP2 fully coupled LGM experiments and CMIP3 future projections (Sutton et al, 2007).…”

Hydrologic impacts of past shifts of Earth’s thermal equator offer insight into those to be produced by fossil fuel CO 2

“…This shift will be the consequence of a difference in the extent of warming in each hemisphere. Model simulations suggest that the Northern Hemisphere, because of its continents, will heat up twice as fast as the Southern Hemisphere, because of its oceans (2)(3)(4). For example, with differential heating of the polar hemispheres, if the extent of global warming was to reach 3.6°C, then that in the north would be 4.8°C and that in the south 2.4°C.…”

“…The thermal inertia of the Southern Ocean has played a large role in the evolution of the differential thermal gradient (49). Accordingly, there are tentative indicators that a northward shift of Earth's thermal equator could already be underway (3,4). For example, drought in the American West (34) and in southern Amazonia (50) is consistent with a northward migration of Earth's thermal equator.…”

A Novel Tool for the Determination of Tropopause Heights by Using GNSS Radio Occultation Data

“…Examples of statistical studies using alternative detection variables include analyses of changes in integrated ocean heat content [3] and Northern Hemisphere sea ice extent [4]. There has also been interest in various temperature-related indices, such as the temperature contrast between land and ocean, low and high latitudes, and the Northern and Southern Hemispheres [5]. Other indices, such as the ''Green-house Climate Response Index'' [6] and the ''Common-Sense Climate Index'' [7], simultaneously consider changes in temperature and moisture.…”

“…It is well known as signals of Global Change are given not only by Earth's temperatures but also by a wide variety of other parameters such as the integrated heat content [3], Northern Hemisphere sea ice extent [4] or to other kind of temperature-related indices: gradient of temperatures between land and ocean, low and high latitudes or North/South Hemisphere [5]. Other kind of fingerprints can be considered the "Greenhouse Climate Response Index [6] and the Common-Sense Climate Index [7] which take into account the coupling of temperature and moisture.…”