Global warming is well underway

The forecast suggests that a climatic “switch” may soon be thrown, resulting in a seismic geothermal shift.

If the prediction is correct, later generations could find themselves living in a climate similar to that of the early Pliocene epoch.

Even though at that time the greenhouse effect of atmospheric carbon dioxide was no greater than it is today, average global temperatures were at least 3C warmer.

Sea levels were 25 metres, or 82ft, higher four million years ago during the early Pliocene. Such a rise would have a devastating effect on human populations around the world, submerging whole islands and coastal cities.

The epoch was also marked by droughts and torrential rains.

Human evolution may have depended on the onset of drier conditions about three million years ago, when ice started spreading in the north and the Earth began to cool. Experts writing in the journal Science say human-induced climate change may already be pushing the “switch”.

Macquarie University PhD students Linda Beaumont and Ian McAllan, together with associate professor Lesley Hughes, have analysed the movements of migratory birds visiting south-eastern Australia since the 1960s.

Using published literature, bird observer reports, and observations of bird watchers, the team compared the arrival date for 24 species and the departure for 12 species over the past 40 years.

The study is believed to be the largest of its kind in the southern hemisphere, and is published in the current edition of the international journal Global Change Biology.

The study found half of the species analysed – which included sandpipers, kingfishers, bee eaters and plovers – showed a significant trend toward earlier arrival since 1960.

It showed they were arriving on average 3.5 days earlier per decade across the whole study group.

At the same time, there was an average delay in departure of 5.1 days per decade.

Scientists rely on proxies to reconstruct paleoclimatic surface temperatures because geographically widespread records of temperatures measured with instruments date back only about 150 years. Other proxies include corals, ocean and lake sediments, ice cores, cave deposits, and documentary sources, such as historic drawings of glaciers. The globally averaged warming of about 1 degree Fahrenheit (0.6 degrees Celsius) that instruments have recorded during the last century is also reflected in proxy data for that time period, the committee noted.

The report was requested by Congress after a controversy arose last year over surface temperature reconstructions published by climatologist Michael Mann and his colleagues in the late 1990s. The researchers concluded that the warming of the Northern Hemisphere in the last decades of the 20th century was unprecedented in the past thousand years. In particular, they concluded that the 1990s were the warmest decade, and 1998 the warmest year. Their graph depicting a rise in temperatures at the end of a long era became known as the “hockey stick.”

The Research Council committee found the Mann team’s conclusion that warming in the last few decades of the 20th century was unprecedented over the last thousand years to be plausible, but it had less confidence that the warming was unprecedented prior to 1600; fewer proxies — in fewer locations — provide temperatures for periods before then. Because of larger uncertainties in temperature reconstructions for decades and individual years, and because not all proxies record temperatures for such short timescales, even less confidence can be placed in the Mann team’s conclusions about the 1990s, and 1998 in particular.

The committee noted that scientists’ reconstructions of Northern Hemisphere surface temperatures for the past thousand years are generally consistent. The reconstructions show relatively warm conditions centered around the year 1000, and a relatively cold period, or “Little Ice Age,” from roughly 1500 to 1850. The exact timing of warm episodes in the medieval period may have varied by region, and the magnitude and geographical extent of the warmth is uncertain, the committee said. None of the reconstructions indicates that temperatures were warmer during medieval times than during the past few decades, the committee added.

The scarcity of precisely dated proxy evidence for temperatures before 1600, especially in the Southern Hemisphere, is the main reason there is less confidence in global reconstructions dating back further than that. Other factors that limit confidence include the short length of the instrumental record, which is used to calibrate and validate reconstructions, and the possibility that the relationship between proxy data and local surface temperatures may have varied over time. It also is difficult to estimate a mean global temperature using data from a limited number of sites. On the other hand, confidence in large-scale reconstructions is boosted by the fact that the proxies on which they are based generally exhibit strong correlations with local environmental conditions. Confidence increases further when multiple independent lines of evidence point to the same general phenomenon, such as the Little Ice Age.

Collecting additional proxy data, especially for years before 1600 and for areas where the current data are relatively sparse, would increase our understanding of temperature variations over the last 2,000 years, the report says. In addition, improving access to data on which published temperature reconstructions are based would boost confidence in the results. The report also notes that new analytical methods, or more careful use of existing methods, might help circumvent some of the current limitations associated with large-scale reconstructions.

The committee pointed out that surface temperature reconstructions for periods before the Industrial Revolution — when levels of atmospheric greenhouse gases were much lower — are only one of multiple lines of evidence supporting the conclusion that current warming is occurring in response to human activities, and they are not the primary evidence.

The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter.

Scientists have found the first hard evidence to show that this actually happened 8,200 years ago, when the climate in parts of the northern hemisphere cooled dramatically after a period of global warming.

Paradoxically, a warmer world could lead to harsher winters in Britain because of the way that melting freshwater from the Greenland ice cap can interfere with the saltwater engine that drives the Gulf Stream

In the Siberian taiga and Canadian Rockies, in Southern California and Australia, researchers find growing evidence tying an upsurge in wildfires to climate change, an impact long predicted by global-warming forecasters.

A team at California’s Scripps Institution, in a headline-making report this month, found that warmer temperatures, causing earlier snow runoff and consequently drier summer conditions, were the key factor in an explosion of big wildfires in the U.S. West over three decades, including fires now rampaging east of Los Angeles.

Researchers previously reached similar conclusions in Canada, where fire is destroying an average of 6.4 million acres a year, compared with 2.5 million in the early 1970s. And an upcoming U.S.-Russian-Canadian scientific paper points to links between warming and wildfires in Siberia, where 2006 already qualifies as an extreme fire season, sixth in the past eight years. Far to the south in drought-stricken Australia, meanwhile, 2005 was the hottest year on record, and the dangerous bush fire season is growing longer.

“Temperature increases are intimately linked with increases in area burned in Canada, and I would expect the same worldwide,” said Mike Flannigan, a veteran Canadian Forest Service researcher….

McClatchy Newspapers

WASHINGTON – It was one of the greatest calamities of all time: Something turned up the Earth’s thermostat, touching off a monstrous heat wave that killed many animals and drove others far from their homes to seek cooler climes.

This catastrophe occurred 55 million years ago, after the age of the dinosaurs and long before humans appeared. But scientists warn that today’s global warming means that it could be happening again.

The ancient hot spell, which lasted 50,000 to 100,000 years, goes by the unwieldy name of Paleocene-Eocene Thermal Maximum. It was caused by a sudden – in geological terms – doubling or tripling of carbon dioxide and other greenhouse gases in the atmosphere. Climate scientists say the result was a massive increase of 10 to 12 degrees Fahrenheit – even higher near the poles – above the prevailing temperature.

“In certain regards, the PETM is very similar to what is happening right now,” said Gerald Dickens, an earth scientist at Rice University in Houston. “Just like now, a huge amount of carbon rapidly entered the ocean or atmosphere. The most notable difference is the rate. Things are happening much faster now than during the PETM.”

Most scientists attribute much of today’s global warming to the burning of carbon-rich fossil fuels in factories, cars and trucks. If the present trend continues, Dickens said, the world will add as much carbon to the atmosphere in 500 years – from 1800 to 2300 – as the PETM did over 10,000 years.
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Professor Peter Cox, of Exeter University, told the Royal Geographical Society annual conference that temperatures could rise 8C by 2100 because of a “compost effect” which could see carbon dioxide levels increase 50 per cent faster than previously estimated.

Currently, around one quarter of carbon emissions are absorbed by the soil and one quarter by the oceans. It had previously been assumed that these proportions would remain the same. But Professor Cox said that global warming is damaging the soil’s ability to absorb carbon emissions.

But that’s the inescapable implication of a piece of research published yesterday by a group of the world’s most distinguished climate scientists. Freak storms such as Hurricane Katrina, which devastated the Big Easy a year ago, are not just freaks, they suggest. They are down to us.

Warmer seas causing more violent hurricanes and typhoons are almost certainly the result of greenhouse gas emissions, they conclude; they are caused, ultimately, by the carbon dioxide from the power station that provides your electricity, from the exhaust of the car you drove to work this morning.
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The 19 scientists, from America, Britain and Germany, include James Hansen of Nasa, the doyen of American climate change researchers, and Professor Phil Jones from the Climatic Research Unit of the University of East Anglia at Norwich.

They said that, in a comprehensive investigation, they had found an 84 per cent probability that human triggers accounted for most of the observed increases in sea surface temperatures (SSTs), during the past century, in the breeding grounds for hurricanes (as they are called in the Atlantic) and cyclones (as they are known in the Pacific).

WASHINGTON (Reuters) – Arctic perennial sea ice — the kind that stays frozen year-round — declined by 14 percent between 2004 and 2005, climate scientists said on Wednesday, in what one expert saw as a clear sign of greenhouse warming.

Researchers have been monitoring the shrinking polar ice cap with satellites since the 1970s. What is new, and remarkable to scientists, is that the decline has been observed in winter as well as summer.

“The greenhouse phenomenon is actually becoming apparent in the Arctic,” said Josefino Comiso of NASA’s Goddard Space Flight Center outside Washington DC. “The winter warming signal is finally coming out.”
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