The increase is not anthropogenic?
Another criticism of the evidence behind climate change being anthropogenic appears more substantiated. Experiments using radiosonde data conducted by Santer et al (1996), agreed with model data and appeared to have found the human influence on global climate, with increased greenhouse gases causing warming. At the time it was published, the paper was heralded as “proof”, and seen as real observed rather than previous climate model predictions. It was at first thought to provide solid evidence for the case of anthropogenic climate change. The results (see fig 1.2) led to the IPCC to state “a discernible human influence on global climate" exists, in the 1995 IPCC report.
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However, the Santer et al. (1996) paper was criticised for not showing the full extent of the data available, and using only the dates which fitted in with the anthropogenic hypothesis. Once placed in context the data doesn’t show an upward trend, but simply a warm period, which can be explained by natural factors, e.g. strong El Nino events occurring at the time period used (Weber, 1996 and Daly, 1997). The full data version published later that year by Michaels and Knappenberger (1996), this time using a longer 38year time period, which extended before and after Santer et al’s results (see fig 1.3), showed the first papers conclusion was a product of the dates chosen. Taking a limited time period allowed the temperature trend to fit with the climate models predictions. It can be seen from these two papers that when looking for underlying data trends, extending the time period makes the results more reliable.
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So it appears incomplete regional temperature records have been used to support global warming, but have failed to withstand criticism by sceptics. However, the evidence is not conclusive as regional temperatures are subject to variation.
A more reliable measurement can be obtained by using average global temperature data. A major problem is that there is variation in the earth’s temperature on a regional basis, and throughout recorded history, causing further debate as to what causes this level of variation. For some the answer may be fluctuations in the sun’s solar activity. This theory again supports the view that climate change is occurring, but is not due to human impacts. When solar magnetic cycles are short, the sun is more active, making it brighter, and consequently the earth is warmer. These variations in the solar cycle correlate with fluctuations in temperature (Soon, Posmentier, and Baliunas, 1996). Bond et al. (2001), produced a report linking climate variability to the sun, with data showing the North Atlantic has warmed and cooled in step with the waxing and waning of the sun. This research definitely produces an alternative to anthropogenic climate forcing. But is evidence conclusive enough to discredit the possibility of a manmade effect on climate?
Most recent research shows that the sun has been more active over the last 70 years than it has been for the previous 8,000 years. However, the study using tree ring analysis says this recent increase in activity cannot account for the global warming observed in the last few decades. This is because even though an increased number of sunspots have been observed, they have relatively little effect on the total energy emitted by the sun. So as sunspot number increases the sun emits a relatively constant amount of energy (Solanki et al, 2004).
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