Tuesday, August 18, 2015
Trenberth restates the faith
He would! He says that natural variability is preventing warming. By that logic, maybe the slight warming of the 20th century was caused by natural variability too. It is all just speculation
There are signs that the planet is heating up, and even 'on fire.' This is according to Dr Kevin Trenberth, a scientist at the US National Center for Atmospheric Research, who claims the global warming 'pause' is now over.
The so-called pause refers to the fact that the temperature of Earth's surface has increased by just 0.06°C in the past 15 years.
It has been used by some groups as evidence that climate change is not happening.
But Dr Trenberth argues that natural variability in weather patterns has masked the upward trend in temperatures, and he says this variability may be about to end.
He points out that in the western region of North America, the prolonged drought has led to high temperatures and many wildfires, from Canada and the Northwest earlier this summer to California more recently.
In the Pacific, hurricanes, typhoons and tropical cyclones have caused havoc, and with several damaging hits in Japan, China and Taiwan, in particular.
Globally, surface temperatures have been setting record high values. US temperatures this year are well above average.
Meanwhile, precipitation has been above average in much of the US outside of the West, making temperatures lower than they otherwise would have been.
In a paper titled, 'Has There Been a Global Warming Hiatus?', Trenberth argues natural variability through of the oceans, atmosphere, land and ice is responsible for the strange weather.
'The warmest year in the 20th century was 1998. However, since then there has been an apparent absence of an increase in global mean surface temperature (GMST) from 1998 through 2013.
'This has become known as the 'hiatus,' said Trenberth, writing in The Conversation. 'While 2005 and 2010 GMST values slightly exceeded the 1998 value, the trend upwards slowed markedly until 2014, which is now the warmest year on record.
'Moreover, there are excellent prospects that 2015 will break that record – the past 12 months through June 2015 are indeed the warmest 12 months on record. 'It looks like the hiatus is over.'
Trenberth says there are major natural variabilities that prevent the global temperature rise from simply being linear.
The main variability is the Pacific Decadal Oscillation - or PDO - in which the planet's largest ocean goes through a cycle of burying heat and then releasing it.
The National Oceanic and Atmospheric Administration says the PDO has gone into a positive phase when stored heat gets released to the atmosphere and across the globe.
'There are major changes in Pacific trade winds, sea level pressure, sea level, rainfall and storm locations throughout the Pacific and Pacific rim countries, but also extending into the southern oceans and across the Arctic into the Atlantic,' said Dr Trenberth.
'There is good but incomplete evidence that these changes in winds alter ocean currents, ocean convection and overturning, which leads to changes in the amount of heat being sequestered at greater depths in the ocean during the negative phase of the PDO.'
'The role of natural variability paints a different picture than one of steadily rising global mean temperatures,' added Dr Trenberth.
'Indeed, the combination of decadal variability plus a heating trend from increasing greenhouse gases makes the GMST record more like a rising staircase than a monotonic climb.'
Posted by John J. Ray (M.A.; Ph.D.).