Global warming causes and resulting climate change

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The most authoritative reports on the causes and consequences of climate change come from the IPCC, particularly its 1995 Second Assessment Report (SAR)

(Bruce et al. 1996; Houghton et al. 1996; Watson et al. 1996) and its 2001 Third Assessment Report (TAR) (IPCC 2001; see Albritton et al. 2001; and IPCC Working Group II 2001). The latter report refined the findings of the first assessment, pointing out that climate change is likely to be worse and occur more rapidly than initially predicted (see National Research Council et al. 2002). Here I summarize the IPCC's findings on global warming and the worldwide effects of climate change before pointing out some of the anticipated socio-economic impacts in East Asia.

According to the IPCC's TAR (Albritton et al. 2001), there is now a collective picture, derived from an increasing body of observations, of a warming world and other changes in the Earth's climate system. The global average surface temperature increased during the twentieth century, with the 1990s and early 2000s the warmest on record (see also WMO 2003). Snow and ice cover have decreased, global average sea level has risen, and the heat content of the oceans has increased. Other aspects of climate have changed during the twentieth century, including changes in precipitation (e.g. increased heavy precipitation events) and cloud cover; fewer extreme low-temperature periods and more high-temperature periods; more frequent, persistent, and intense episodes of the El NiƱo ocean-warming event (and related adverse effects on weather in many areas); and an increase in areas experiencing drought and severe wet periods. Some climate related events, such as tornadoes or tropical storms, do not appear to have changed based on IPCC data, although the evidence is conflicting.

The TAR also finds that emissions of GHGs from human activities are altering the atmosphere in ways that are expected to affect climate. Human activities have increased atmospheric concentrations of GHGs (e.g. CO2, methane, nitrous oxide, halocarbons) and their warming potential. According to the report, "atmospheric concentration of carbon dioxide (CO2) has increased 31 percent since 1750. The present CO2 concentration has not been exceeded during the past 420,000 years and likely not during the past 20 million years. The current rate of increase is unprecedented during at least the past 20,000 years" (Albritton et al. 2001: 7). Three-quarters of human-induced emissions of CO2 over the last two decades has come from the burning of fossil fuels (e.g. coal, oil, and natural gas), with most of the remainder the consequence of land-use changes, particularly deforestation. Natural causes of climate change have been relatively small. Furthermore, models for predicting future climate are increasingly accurate and precise. While uncertainties remain, understanding of climate processes and predicted effects has improved.

According to the TAR, new and stronger evidence points to human activities as the sources of observed global warming over the last fifty years, further strengthening the SAR's conclusion that the "balance of evidence suggests a discernible human influence on global climate" (IPCC 1995). Warming over the last 100 years is unlikely to have been natural, with studies showing that global warming, particularly during the last 35-50 years, most likely resulted from human activities. Thus, the TAR concludes: "In light of new evidence and taking into account the remaining uncertainties, most observed warming over the last fifty years is likely to have been due to the increase in GHG concentrations. Furthermore, it is very likely that the 20th century warming has contributed significantly to the observed sea level rise... and widespread loss of land ice" (Albritton et al. 2001: 10).

Furthermore, the TAR determined that human activities will continue to shape the Earth's atmosphere throughout this century and into the future, and average global temperatures and sea levels are projected to rise. Emissions from burning fossil fuels will be the dominant source of atmospheric CO2 during this century. These emissions and those of other GHGs would have to be reduced to "a very small fraction of current emissions" to stabilize climate (Albritton et al. 2001: 12). Global average temperature is projected by the IPCC to increase by 1.4-5.8 degrees Celsius during this century (more than anticipated in the SAR). This warming will occur at a rate faster than that observed in the twentieth century, "very likely to be without precedent during at least the last 10,000 years" (Albritton et al. 2001: 13). During this century, warming is expected to occur in most areas, but it should be particularly pronounced at northern high latitudes during winter. Global mean sea level is expected to rise 0.09-0.88 meters in this century, with other very likely changes to include higher maximum temperatures and more hot days over most land areas, higher minimum temperatures and fewer cold days over most land areas, more intense precipitation events over many areas, increased summertime continental drying and drought over mid-latitude continental interiors, and more severe storms over some areas.4

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