Latest report refutes global warming ‘hiatus’
THERE has been no slow-down in the rate of global warming, and claims of a so-called “hiatus” in the rising global temperature are no longer valid.
This is the finding of a new study by the US National Oceanic and Atmospheric Administration (Noaa) in the journal Science, in which scientists say the rate of global warming during the last 15 years has been as fast – or faster – than that seen during the last half of the 20th century.
The study refutes a statement in the Intergovernmental Panel on Climate Change’s (IPCC) fifth assessment report, which said the global surface temperature had shown a much smaller increase between 1998-2012 than it had over the past 30 to 60 years.
Noaa said the apparent slow-down, nicknamed a ”hiatus”, had inspired “a suite of physical explanations for its cause, including changes in radiative forcing, deep-ocean heat uptake and atmospheric circulation changes”.
But improvements in the quality of temperature records, and the inclusion of the last two years of temperature data, contradict the IPCC report.
Lead author Thomas Karl, director of Noaa’s centre for environmental information, said while the theories about the so-called hiatus had merit in helping to understand the global climate system, other important aspects – such as observational biases in temperature data – had not got the same amount of attention.
Now, with recent improvements in the observed temperature record, and with the inclusion of temperatures for 2013 and 2014 – the hottest on record – they have re-examined the evidence and found there had been no slow-down.
Temperature measurements are taken by thousands of commercial ships and buoys which drift on the ocean surface. Those from buoys are generally cooler than those from ships. To compare the two over the long term, they need to be compatible. Noaa scientists developed a method to do so, using it in their analysis.
There have also been advancements in the calculation of land-surface temperatures, especially the release of the International Surface Temperature Initiative databank.
The researchers said this more than doubled the number of recording stations available, and improved coverage over the Arctic, where temperatures rose rapidly in recent decades. Incomplete recording in the Arctic had led to an underestimate of warming since 1997.