Ancient climate change 'link' to CO2

A "global pattern" of change in the Earth's climate began 2.7 million years ago, say scientists.

Researchers found that, at this point, temperature patterns in the tropics slipped into step with patterns of Ice Ages in the Northern Hemisphere.

They report in the journal Science that atmospheric CO2 could be the "missing link" to explain this global pattern.

The findings, they say, reveal a "feedback process" that could have been magnified by greenhouse gases.

This loop of feedback could have intensified both the Ice Ages in the Northern Hemisphere, and temperature fluctuations in the tropics.

Professor Timothy Herbert from Brown University in Rhode Island, US, led the research. He and his colleagues, in the US and China, analysed mud cores from the seabed in the four tropical ocean basins - the Arabian Sea, the South China Sea, the eastern Pacific and the equatorial Atlantic Ocean.

These mud cores are laid down over millions of years - as sediments of dead plant and animal material sink to the ocean floor.

So by analysing the chemical composition of this material - specifically the chemical remains of one ancient and tiny marine organism - the scientists were able to produce a timeline of temperature changes.

The team "found a fingerprint in the sequence of temperature changes" - a pattern that began 2.7 million years ago, Professor Herbert explained.

He told: "The timing and the amplitude of temperature changes [in the Northern Hemisphere] are reproduced in the tropical temperatures. The patterns are incredibly similar."

He added that the study provided the first direct evidence of a global pattern in climate change that dated back almost three million years.
Ancient greenhouse

Professor Herbert added that the "best global mechanism" to explain this link was the level of atmospheric greenhouse gases.

Dr Carrie Lear, a palaeoclimate scientist from Cardiff University in the UK, agreed that carbon dioxide was the likely "culprit".

She told: "This study reveals a feedback process that has magnified climate change since the inception of Northern Hemisphere glaciation 2.7 million years ago.

"It seems the tropical warming caused by high CO2 levels set off a chain of events resulting in additional greenhouse gases, including water vapour, being released to the atmosphere, thus causing further warming."

Dr Lear said that such studies of past climate change were "invaluable in understanding the current climate system, and hence predicting future change".

Climate change 'makes birds shrink' in North America

Songbirds in the US are getting smaller, and climate change is suspected as the cause.
A study of almost half a million birds, belonging to over 100 species, shows that many are gradually becoming lighter and growing shorter wings.
This shrinkage has occurred within just half a century, with the birds thought to be evolving into a smaller size in response to warmer temperatures.
However, there is little evidence that the change is harmful to the birds.
Details of the discovery are published in the journal Oikos.In biology, there is a general rule of thumb that animals tend to become smaller in warmer climates: an idea known as Bergman's Rule.
Usually this trend can be seen among animal species that live over a range of latitude or altitude, with individuals living at more northern latitudes or higher up cooler mountains being slightly larger than those below, for example.
Quite why this happens is not clear, but it prompted one group of scientists to ask the question: would animals respond in the same way to climate change?
To find out, Dr Josh Van Buskirk of the University of Zurich, Switzerland and colleagues Mr Robert Mulvihill and Mr Robert Leberman of the Carnegie Museum of Natural History in Rector, Pennsylvania, US decided to evaluate the sizes of hundreds of thousands of birds that pass through the Carnegie Museum's Powdermill ringing station, also in Pennsylvania.They examined the records of 486,000 individual birds that had been caught and measured at the ringing station from 1961 to 2007.
These birds belonged to 102 species, arriving over different seasons. Each was weighed. It also had the length of its wings measured, recorded as wing chord length, or the distance between the bird's wrist to the tip of the longest primary feather.
Their sample included local resident bird species, overwintering species, and even long distance migrants arriving from the Neotropics.
What they found was striking.
Of 83 species caught during spring migration, 60 have become smaller over the 46 year study period, weighing less and having shorter wings.
Of the 75 species migrating in autumn, 66 have become smaller.In summer, 51 of 65 breeding species have similarly reduced in size, as have 20 out of 26 wintering species.
The differences in size are not big.
"On average, the decline in mass of spring migrants over the 46 year study was just 1.3%," says Dr Buskirk.
"For a 10g warbler that's a loss of just 130mg."
But some species are losing more weight.
For example, the rose-breasted grosbeak has declined in mass by about 4%, while the Kentucky warbler has dropped 3.3% in weight and the scarlet tanager 2.3%.
The trend is particularly noticeable among those birds that winter in the New World tropics of the Caribbean, Central America and South America.
"The headline finding is that the body sizes of many species of North American birds, mostly songbirds, are gradually becoming smaller," says Dr Buskirk.
However, their populations are not dwindling."So many of these species are apparently doing just fine, but the individual birds are becoming gradually smaller nonetheless," says Dr Buskirk.
That suggests that bird species in North America are obeying Berman's rule, by evolving into a smaller size as temperatures increase.
Though this change appears quick, it has taken place over at least 20 generations of birds.
"There are plenty examples of rapid contemporary evolution over much shorter time periods," says Dr Buskirk.
Whether the trend will cause the birds any long-term consequences is unclear.
"In one obvious sense, the consequences are positive," says Dr Buskirk.
"That is, as temperatures become warmer, the optimal body size is becoming smaller."
However, even though the species appear to be adapting to the new climatic conditions, it could still be that their average "fitness" in evolutionary terms, is going down."Evidence from other studies is that some species will benefit and others will be harmed, and it's not always the species we like that will be harmed," says Dr Buskirk.
The jury is still out as to why any species responds to warmer temperatures by becoming smaller.
Originally, biologists proposed that having a larger body surface to volume might help in warmer climates.
But more recent ideas suggest that animals might actually be responding instead to something else that correlates with temperature, such as the availability of food, or metabolic rate.
"It looks like it might take a while before we know," says Dr Buskirk.
His team says much more data is now needed to confirm this trend and to see if it is happening in animals other than birds.
For example, it took an avalanche of data before people became convinced that climate change is already altering when birds start migrating.