"Ocean's 'Thermostat' May Moderate Global Warming"
"Ocean's 'Thermostat' May Moderate Global Warming"by Jason McManus
"The Earth's temperature may stay roughly the same for a decade, as natural climate cycles enter a cooling phase, scientists have predicted. A new computer model developed by German researchers, reported in the journal "Nature," suggests the cooling will counter greenhouse warming. However, temperatures will again be rising quickly by about 2020, they say.
"One message from our study is that in the short term, you can see changes in the global mean temperature that you might not expect given the reports of the Intergovernmental Panel on Climate Change (IPCC)," said Noel Keenlyside from the Leibniz Institute of Marine Sciences at Kiel University.
The key to the new prediction is the natural cycle of ocean temperatures called the Atlantic Multidecadal Oscillation (AMO), which is closely related to the warm currents that bring heat from the tropics to the shores of Europe. The cause of the oscillation is not well understood, but the cycle appears to come round about every 60 to 70 years. Imagine the payoff of knowing with some certainty what the next 10 years hold in terms of temperature and precipitation.
Keenlyside explained that since record keeping began in the 19th century, the North Atlantic climate has changed in natural cycles that last a decade or more. These shifts are likely associated, at least in part, with natural variations in ocean currents. A new forecasting model, based on past and present sea surface temperatures, suggests the imminent onset of a cool-down cycle for currents in both the North Atlantic and tropical Pacific. Keenlyside and colleagues, whose study appears in the journal "Nature," hope to further quantify this effect and incorporate it into future climate predictions on the decade scale. "I think it's just naive to think that there won't continue to be multi-decadal fluctuations in the climate," he said. Ocean current systems move heat around the globe, but they do not remain static. Their fluctuations are largely driven by seawater density, which is in turn governed by factors like temperature and salinity.
The massive North Atlantic current called the thermohaline circulation brings warm water north, where it releases its heat, and then transports cooled water south again. When this current is naturally strong, climate in the North Atlantic warms. Sea surface temperatures in the tropical Pacific will remain unchanged. Natural climate changes may offset human-caused global warming over the next decade, keeping ocean temperatures the same or even temporarily cooling them slightly. This short-term situation might create a problem if policymakers regarded it as a sign they could ease efforts to limit greenhouse gases or play down global warming. "The natural variations change climate on this timescale and policymakers may either think mitigation is working or that there is no global warming at all," said Keenlyside.
Parts of North America and Europe may cool naturally over the next decade, as shifting ocean currents temporarily blunt the global-warming effect caused by mankind. Average temperatures in areas such as California and France may drop over the next 10 years, influenced by colder flows in the North Atlantic.A temporary weakening of the ocean current which regulates global temperatures will see a slight cooling in Europe and North America, masking the effects of human-induced climate change say German researchers. Long-term climate changes in the North Atlantic region affect "hurricane activity in the Atlantic, and surface temperature and rainfall variations over North America, Europe and northern Africa,'' according to the study."
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