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Tuesday 8 April 2008 (Updated Wed 16 April 08)

RAPID ROUNDUP: Is the Earth cooling? – experts respond.

There has been some discussion and a little confusion in the media lately about whether the Earth has in fact been cooling or warming in recent times. The World Meteorological Organisation recently put out a statement on this topic, Temporary La Niña's cooling effect does not stall global warming (Info Note No. 44). Australian experts comment below.

Several climate experts from the National Climate Centre at the Bureau of Meteorology have also prepared a scientific analysis of the issue, Waiting for Global Cooling.

Feel free to use these comments in your stories. If you would like to speak to one of these or other experts, please don’t hesitate to contact us on (08) 8207 7415 or by email.

Read comments from (in alphabetical order):

Professor Barry Brook is Sir Hubert Wilkins Chair of Climate Change and Director of the Research Institute for Climate Change and Sustainability at the University of Adelaide.

Dr Robert Fawcett and Dr David Jones are from the National Climate Centre at the Bureau of Meteorology. See full analysis.

Dr Andrew Glikson is an Earth scientist at the Australian National University in Canberra, involved in the study of the effects of atmospheric changes on the mass extinction of species.

William Kininmonth is a meteorologist and an outspoken critic of global warming and the Kyoto Protocol. He was head of the National Climate Centre at the Bureau of Meteorology from 1986 to 1998.

Dr Helen McGregor is an Associate Research Fellow at the University of Wollongong in NSW and has expertise in La Niña/El Niño, oceanography and climates of the past.

Professor Neville Nicholls is in the School of Geography & Environmental Science at Monash University in Melbourne, and was a member of the writing team for the IPCC Synthesis Report.

Professor Barry Brook is Sir Hubert Wilkins Chair of Climate Change and Director of the Research Institute for Climate Change and Sustainability at the University of Adelaide.

"Claims that global warming stopped in [... insert convenient year] underscore a fundamental lack of understanding about the difference between a trend and variability - or else a deliberate attempt to mislead people with the intent of further delaying action on climate change.

The trend for global warming is consistently upwards, but in any given month, or even season or year, the actual temperature will be variable.

Let me illustrate by example. Based on the NASA GISS global meteorological station data, January 2008 was 'cool', at only +0.31°C above the 1950-1980 average. But March 2008 was back to +0.81°C. By comparison, January 1998 was +0.57°C and March 1998 was +0.70°C. In the northern hemisphere, March 2008 was the 2nd warmest month on record (relative to the average), with a +1.40°C anomaly (for reference, the hottest month on record was January 2007 at +1.61°C).

The point is, there is a lot of month-to-month variability, whatever month you happen to cherry pick. But the trend is consistently upwards - all of the above temperature anomalies are greater than the 1950-1980 average, by +0.3 to +1.6°C.

2008 is expected to be a slightly cooler year than 2007, largely because of a particularly intense La Niña and the current low solar activity.

Indeed, recent work has shown that the average temperature difference between the top and bottom of the 11-year solar cycle is almost 0.2°C (we are currently at the bottom). Looking forwards, recent predictions from the UK Hadley Centre are that at least half of the years between 2009 and 2014 will exceed the highest yearly global temperature to-date."

Dr Robert Fawcett and Dr David Jones are from the National Climate Centre at the Bureau of Meteorology. See full analysis.

"There is very little justification for asserting that global warming has gone away over the past ten years, not least because the linear trend in globally-averaged annual mean temperatures (the standard yardstick) over the period 1998-2007 remains upward. While 1998 was the world’s warmest year in the surface-based instrumental record up to that point in time, 2005 was equally warm and in some data sets surpassed 1998.

A substantial contribution to the record warmth of 1998 came from the very strong El Niño of 1997/98 and, when the annual data are adjusted for this short-term effect (to take out El Niño’s warming influence), the warming trend is even more obvious."

Dr Andrew Glikson is an Earth scientist at the Australian National University in Canberra, involved in the study of the effects of atmospheric changes on the mass extinction of species.

"Some advocates of the 'pro-Carbon lobby' use climate data selectively, namely, they use low seasonal or annual points below the average trend as 'evidence' for cooling, and high points above the average trend to say that subsequent years represent a 'cooling'.

Moreover, climate projections show that, as the globe warms, extreme weather events ensue. For example as a result of collision between warm tropical ocean and air currents and cold water and air masses associated with ice melting and southward migration of ice melt water.

In the extreme this threatens to result in the abortion of the Gulf Stream, triggering several degrees drop in temperature over western Europe and NE America, as has repeatedly occurred during the recent glacial-interglacial history of the Earth.

No doubt if (God forbid) this happens, climate denialists will claim 'global cooling'...

It is essential to make a distinction between climate trends and annual or even multi-annual variations, as based on advanced studies of the recent climate history of Earth. Mammals flourished on land only since CO2 levels declined below about 450 parts per million about 34 million years ago, with subsequent decline of mean deep sea temperatures below 6°C and onset of polar ice sheets. Prior to about 11,500 years ago hunter-gatherer humans had to repeatedly migrate as glacial and interglacial eras interchanged, and could only commence agriculture from about 8,500 years ago (the Neolithic) once climate conditions stabilised.

The atmosphere is extremely sensitive to forcing by minor levels of greenhouse gas, which affect the physical and chemical processes and energy level of the atmosphere-ocean-biosphere system, including interchange of CO2, CH4 and oxygen between vegetation and animals. The forced anthropogenic release of over 300 billion tons of carbon into the atmosphere since the dawn of the industrial age, raising CO2 levels to near 390 ppm (near-40% over the maxima of the last one million years), has severely upset this delicate balance, raising the atmospheric energy levels by some 1.6 Watt/square metres and threatening to return the Earth's climate to conditions which existed three million years ago (mid-Pliocene), when temperatures were 2-3 degrees higher than at present and sea level higher by some 25+/-12 metres."

William Kininmonth is a meteorologist and an outspoken critic of global warming and the Kyoto Protocol. He was head of the National Climate Centre at the Bureau of Meteorology from 1986 to 1998.

"Info Note No. 44 issued by the World Meteorological Organization (WMO) underscores why the public should take no notice of climate predictions for months, years or centuries ahead.

In the Note, the Secretary General of WMO discussed the potential for the current La Niña to extend into a second year and then concluded, with remarkable candidness, that 'The likelihood of the current La Niña continuing for such a period will remain unclear for some months'. Clearly the climate scientists, with all their elaborate computer models, cannot predict even a few months in advance.

It should be recalled that in January 2007 the UK Meteorological Office, with much fanfare, predicted that the then current El Niño event would continue through 2007 and that 2007 would be the warmest year on record. The prediction was spectacularly wrong. The El Niño was soon replaced by a La Niña event and the global temperature fell 0.6°C in the 12 months to January 2008, effectively wiping off a century of ‘global warming’.

1998 remains the warmest year of the climate record and the headline beginning 'Global warming continues...' is clearly misleading. No amount of spin can disguise the fact that there are many unknowns and uncertainties about the climate system. There is no compelling evidence that carbon dioxide has any significant control over the direction of global temperature and climate. The processes that regulate the interannual to decadal fluctuations of climate are poorly understood and, as yet, unpredictable."

Dr Helen McGregor is an Associate Research Fellow at the University of Wollongong in NSW and has expertise in La Niña/El Niño, oceanography and climates of the past.

"What the WMO statement is saying is that the current La Niña represents a short-term fluctuation on an overall warming trend. We must be clear here: we are still experiencing global warming. The average global temperature for January and February 2008, despite the influence of La Niña, is over 0.1 degrees Celsius warmer than the 1961-1990 baseline period.

If you start looking further back in time the 2008 temperatures are even more unusual, for example, they are more than half a degree Celsius higher than the average for the 1850s. Importantly, we still have nine months of 2008 left, during which time the La Niña is likely to wane meaning temperatures can rise again. The issue of warming versus cooling can cause confusion when short-term climate swings are mixed with long-term changes – climate swings must be put into perspective."

Professor Neville Nicholls is in the School of Geography & Environmental Science at Monash University in Melbourne, and was a member of the writing team for the IPCC Synthesis Report.

"Although global average temperatures have increased about 0.75°C since since about 1960, the global average dropped back about 0.5°C over the past year. This drop was caused by what appears to be the strongest La Niña we have seen for about 30 years, judging on the values of the Southern Oscillation Index (SOI) over the past summer.

Similar drops in global temperature have occurred in the past during La Niña events, but in the past the long term warming continued again once the effects of the La Niña subsided. Some commentators have confused this recent, short term La Niña cooling with the long term warming human activity is causing. Just as one cold Melbourne day doesn't show the world has stopped warming, neither does the short-term cooling caused by a La Niña."