Impacts of anthropogenic climate change many, varied

Impacts from warming are evident in satellite images showing that lakes in Siberia disappearing as the permafrost thaws and lake water drains deeper into the ground. Credit: NASA Earth Observatory A new study led by NASA links anthropogenic climate change to a wide range of effects. The study involved scientists from about a dozen institutions and agencies, and looked at biological impacts arising from global temperature increase since the 1970s. The article is published in Nature. According to lead author Cynthia Rosenweig, "This is the first study to link global temperature data sets, climate model results, and observed changes in a broad range of physical and biological systems to show the link between humans, climate, and impact ... Humans are influencing climate through increasing greenhouse gas emissions and the warming is causing impacts on physical and biological systems that are now attributable at the global scale and in North America, Europe, and Asia.

From the abstract of the paper:

Significant changes in physical and biological systems are occurring on all continents and in most oceans.... Most of these changes are in the direction expected with warming temperature. Here we show that these changes in natural systems since at least 1970 are occurring in regions of observed temperature increases, and that these temperature increases at continental scales cannot be explained by natural climate variations alone. Given the conclusions from the ... IPCC ... Report that most of the observed increase in global average temperatures since the mid-twentieth century is very likely to be due to the observed increase in anthropogenic greenhouse gas concentrations, and furthermore that it is likely that there has been significant anthropogenic warming over the past 50 years averaged over each continent except Antarctica, we conclude that anthropogenic climate change is having a significant impact on physical and biological systems globally and in some continents.

Most of the available data are concentrated in North America and Europe. Even so, the data analyzed used nearly 30,000 sets of data documented in about eighty studies, addressing the years 1970 to 2004.

The study involved dividing the planet into observation units (cells) and recording temperature changes and environmental effects in those units. The following is part of one of the graphics supplied with the study. Pinkish colored cells have warmed, blue have cooled, and the whitish and yellowish cells have changed only a little or not at all (yellow = a little warming).

The main outcome of this report is to make clear the idea that the effects of global warming are not something of the future. While future impacts are of course likely, there have already been significant impacts. The distribution of permafrost and its very significant effects are well documented, for instance.

When permafrost melts, the layer of loose soil deepens and trees lose their foundations and tip over. Similar impacts across Earth are likely due to human-caused climate change. Credit: Jon Ranson Other changes include shrinking of glaciers, lake and river temperature increases, and bird migratory patterns changing. The communities of plankton and fish in the ocean (and other bodies of water) are shifting in their species makeup owing to the favoring of warm-adapted species. All in all, the study concludes taht about 90 percent of the observed changes in biological and physical systems are consistent wiht what is expected under warming conditions. Furthermore, other sources of change (such as deforestation) are seen in this study as having had less of an impact than warming for many effects. (But keep in mind that this would not liely apply to tropical deforestation owing to the limitations of the study.)

Changes in timing of plant seasonal events has probably also occurred, though the data on this is less clear.

Regarding the bias in available data, the study concludes:

Documentation of observed changes in physical and biological systems in tropical and subtropical regions is still sparse. These areas include Africa, South America, Australia, Southeast Asia, the Indian Ocean and some regions of the Pacific. One reason for this lack of documentation might be that some of these areas do not have pronounced temperature seasons, making events such as the advance of spring phenology less relevant. Other possible reasons for this imbalance are a lack of data and published studies, lag effects in responses, and resilience in systems. Improved observation networks are urgently needed to enhance data sets and to document sensitivity of physical and biological systems to warming in tropical and sub-tropical regions, where many developing countries are located.

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Rosenzweig, C., Karoly, D., Vicarelli, M., Neofotis, P., Wu, Q., Casassa, G., Menzel, A., Root, T.L., Estrella, N., Seguin, B., Tryjanowski, P., Liu, C., Rawlins, S., Imeson, A. (2008). Attributing physical and biological impacts to anthropogenic climate change. Nature, 453(7193), 353-357. DOI: 10.1038/nature06937

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