Why Global Warming Is Taking A Break b4in.org/p7ds The average temperature on Earth has barely risen over the past 16 years. ETH researchers have now found out why. And they believe that global warming is likely to continue again soon. The number of sunspots (white area here) varies in multi-year cycles. As a result, solar irradiance, which influences the Earth’s climate, also fluctuates. The photo shows a UV image of the sun. Image: Trace Project / NASA Global warming is currently taking a break: whereas global temperatures rose drastically into the late 1990s, the global average temperature has risen only slightly since 1998 – surprising, considering scientific climate models predicted considerable warming due to rising greenhouse gas emissions. Climate skeptics used this apparent contradiction to question climate change per se – or at least the harm potential caused by greenhouse gases – as well as the validity of the climate models. Meanwhile, the majority of climate researchers continued to emphasize that the short-term ‘warming hiatus’ could largely be explained on the basis of current scientific understanding and did not contradict longer term warming. Researchers have been looking into the possible causes of the warming hiatus over the past few years. For the first time, Reto Knutti, Professor of Climate Physics at ETH Zurich, has systematically examined all current hypotheses together with a colleague. In a study published in the latest issue of the journal Nature Geoscience, the researchers conclude that two important factors are equally responsible for the hiatus. El Niño warmed the Earth One of the important reasons is natural climate fluctuations, of which the weather phenomena El Niño and La Niña in the Pacific are the most important and well known. “1998 was a strong El Niño year, which is why it was so warm that year,” says Knutti. In contrast, the counter-phenomenon La Niña has made the past few years cooler than they would otherwise have been. Although climate models generally take such fluctuations into account, it is impossible to predict the year in which these phenomena will emerge, says the climate physicist. To clarify, he uses the stock market as an analogy: “When pension funds invest the pension capital in shares, they expect to generate a profit in the long term.” At the same time, they are aware that their investments are exposed to price fluctuations and that performance can also be negative in the short term. However, what finance specialists and climate scientists and their models are not able to predict is when exactly a short-term economic downturn or a La Niña year will occur. Longer solar cycles More b4in.org/p7ds
Posted on: Tue, 19 Aug 2014 19:00:10 +0000
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