Ocean playing role in absorbing excess heat.
A recent ‘pause’ in global warming, shown through a fall in the rate at which global surface temperatures has risen over the past fifteen years, could be explained by the cooling sea-surface temperatures in the tropical Pacific Ocean. This finding is a step forward in helping to understand why global surface temperatures have risen more slowly in the past fifteen years than previously.
Scientists have been exploring various explanations for the hiatus, such as a reduction in energy reaching Earth, a decline in the amount of heat-trapping water vapour in the stratosphere, and an increase in atmospheric levels of sun-blocking particles produced by volcanoes and industries. A new study then found that effects of one of the world’s biggest ocean circulatory systems, the Pacific decadal oscillation, (a pattern of change in the Pacific Ocean’s climate) had led to waters in the eastern tropical regions of the Pacific to be cooler in recent years. According to scientists, the system is now in a ‘cooling phase,’ which could last for many years. The last phase lasted from the 1940s into the 1970s.
Using computer models, researchers compared their results with observations and found that annual global average temperatures are lower than they would be without the oscillation. In winter, the oscillation affects the Northern Hemisphere by depressing temperatures slightly. In summer, the cooler waters have less of an impact. Observed higher summer temperatures in recent years show the true effects of global warming—effects that should not be ignored. Global average temperatures are taken over the whole year, which obscure the effect.
According to Scripps Institution of Oceanography Professor of Environmental Science Shang-Ping Xie, the Pacific’s grip on the Northern Hemisphere loosens in the summer, allowing for increased greenhouse gases. These continue to raise temperatures and the effects of global warming, such as heat waves and retreating Arctic ice.
The ‘pause’ in global warming linked to the Pacific oscillation was found through a study conducted by the Scripps Institution, and was supported by the US government’s National Oceans and Atmospheric Administration.
The study was done in an effort to reconcile contradictory data about regional and global temperature trends. Climate change skeptics have used the ‘hiatus’ to discredit global warming, but according to professor Xie, the results of this study only bolster the link between greenhouse gases and climate change. It is unclear how long the Pacific will endure its ‘cool phase’, but Xie says that “the wake-up call is going to come some day when the Pacific Ocean decides to swing into a warmer state.”