Dana Nuccitelli: The remaining climate change uncertainties point toward higher risks and greater urgency for action
President-elect Donald Trumps nominee for Secretary of State and until recently the Ceo of ExxonMobil Rex Tillerson was given a confirmation hearing by the Senate Foreign Relations Committee last week. In his testimony, Tillerson accepted the reality of human-caused global warming and that The hazard of climate change does exist and the results of it could be serious enough that action should be taken.
While he accepted the problem exists, Tillerson nevertheless proceeded to downplay its risks, saying:
The increase in the greenhouse gas concentrations in the atmosphere are having an effect, our ability to predict that effect is very limited .
Many climate scientists took issue with that statement, and for good reason. Climate models have been very accurate in their projections about many consequences of human carbon pollution. Its true that theres uncertainty in just how quickly some of those outcomes will be triggered. The bad news is that recent studies have shown that many of those outcomes are happening more quickly than climate scientists anticipated. Greater climate uncertainty translates into more urgency to tackle the problem , not less.
The Gulf Stream could shut down sooner than anticipated
The Gulf Stream which keeps the UK and surrounding area significantly warmer than it would otherwise be is part of the Atlantic Meridional Overturning Circulation( AMOC ). Research has shown it could shut down as a result of global warming 😛 TAGEND
In 1997, the oceanographer Wallace Broecker, of Columbia University in New York, suggested that if the Gulf stream turned off, winter temperatures in the British Isles could fall by an average of 11 C – plunging Blackpool or Berwick to the same temperatures as Spitsbergen, inside the Arctic circle. Any dramatic drop in temperature could have devastating implications for agriculture – and for Europes ability to feed itself .
Just how quickly such a shutdown could happen has been a subject of debate and research among climate scientists. A study published in Science Advances in early January corrected for a bias recently identified in climate models that acted to keep the AMOC and Gulf Stream more stable than it appears to be in reality 😛 TAGEND
Freshwater continually flows into the northern Atlantic through precipitation, rivers and ice-melting. But furnish of salty waters from the south, through the Gulf Stream System, balances this. If however the present slackens, there is less salt supply, and the surface ocean get less salty. This fresher water is lighter than saltier water and therefore cannot sink into the depths so easily. Since this sinking the so-called deep water formation drives the Gulf Stream System, the present continues to weaken. There is a critical point when this becomes an unstoppable vicious cycle. This is one of the classic tip-off phases in the climate system .
In most climate models, the AMOC imports fresh water, which would attain the circulation more stable. According to recent observational data, the AMOC is actually exporting fresh water. The authors of the study corrected for this bias, and ran the models in a scenario of an abrupt doubling of atmospheric carbon dioxide levels from about 350 to 700 ppm.
This is a more extreme scenario than a more gradual ramping up of carbon levels, but importantly, such studies did not account for meltwater flowing into the Atlantic from the melting Greenland ice sheet. Recent research has shown that Greenland meltwater may significantly weaken the AMOC in the coming decades.
Under the studys scenario, the AMOC lost a third of its strength after 100 years, and broke down within about 300 years. As a result, average winter temperatures over parts of northern and western Europe would become 7C colder than today.
Arctic and Antarctic ice is melting fast
Global sea ice has also been tracking at record-shattering low levels.