Rapid ocean heating heralds weather chaos
Weather across the globe is being changed by the rapid rise in the temperature of the oceans, scientists believe. Jonathan Leake reports.
BRITAIN’S bad summer weather could be linked to a rise in the temperature of the world’s oceans, scientists have warned. They have found that the temperatures of the top 700 metres of the oceans have risen by about 0.3 degrees Celsius since 1955, with most of the rise happening in the past two decades.
The North Atlantic, where the weather systems that affect Europe mostly form, has warmed even more, by an average of 0.5C during the same period.
The rise may seem small, but spread over the breadth and depth of the ocean it represents a huge store of heat that has powerful effects on ocean circulation and weather, sharply increasing the risk of storms and extreme weather.
‘‘This warmth can be linked to rising sea levels and to changes in climate and weather,’’ said Gregory Johnson, a senior scientist with the United States’ National Oceanic and Atmospheric Administration who has co-authored a report on the rising ocean heat.
One key consequence could be more rain.
‘‘The warmer ocean evaporates more easily. It also warms the air above it. For each degree of extra warmth, the air can hold up to 7 per cent more water,’’ said Johnson, whose work was published in State of the Climate in 2011, a US government report to which Britain’s Met Office contributed.
That same warmth could be helping to melt the Arctic ice cap, which has decreased in area by about a third.
Its shrinkage has, in turn, been linked to the southward shift of the jet stream that has left Britain facing its wettest summer on record.
The scale of the extra heat stored in the world’s oceans is stupendous and rising. Johnson calculates the rate of increase as about equal to 12 times our rate of energy use.
Kate Willett, a senior climate scientist at the Met Office who helped edit the report, said: ‘‘The long-term trend has been for the oceans to get steadily warmer. It means there is a lot more energy in the system and that means more evaporation, more rainfall and possibly more wind.’’
For humanity the consequence is that extreme weather, such as this summer’s downpours in the UK, become more likely.
In 2011, the year covered by the report, Britain had its warmest spring and its second-warmest year (behind 2006) since records began.
Records were set in other parts of the world, too.
Why is the ocean warming? Johnson and Willett link this to the rising levels of CO and other greenhouse gases.
‘‘Oceans are getting warmer because the Earth’s radiation budget is no longer in balance,’’ said Johnson.
‘‘We are retaining a little more heat and radiating less out into space because of the blanketing effect of greenhouse gases.
‘‘Most of that heat goes warming the oceans.’’
into