Climate change human link evidence 'stronger'

A review from the UK Met Office says it is becoming clearer that human activities are causing climate change.

It says the evidence is stronger now than when the Intergovernmental Panel on Climate Change carried out its last assessment in 2007.

The analysis, published in the Wiley Interdisciplinary Reviews Climate Change Journal, has assessed 110 research papers on the subject.

It says the Earth is changing rapidly, probably because of greenhouse gases.

In 2007 the IPCC's report concluded that there was "unequivocal" evidence that the Earth was warming and it was likely that it was due to burning of fossil fuels.

Since then the evidence that human activities are responsible for a rise in temperatures has increased, according to this new assessment by Dr Peter Stott and colleagues at the UK Met Office.

The Met Office study comes at a time when some have questioned the entire basis of climate science following recent controversies over the handling of research findings by the IPCC and the Climate Research Unit at the University of East Anglia.

Dr Stott denies that the study has been published as part of a fight back by the climate research community.

"We started writing this paper a year ago. I think it's important to communicate to people what the science is showing and that's why I'm talking about this paper."

'Consistent picture'

The study, which looks at research published since the IPCC's report, has found that changes in Arctic sea ice, atmospheric moisture, saltiness of parts of the Atlantic Ocean and temperature changes in the Antarctic are consistent with human influence on our climate.

"What this study shows is that the evidence has strengthened for human influence on climate and we know that because we've looked at evidence across the climate system and what this shows very clearly is a consistent picture of a warming world," said Dr Stott.

The study brings together other research from a range of disciplines."We hadn't [until now] looked in detail at how the climate system was changing," says Dr Stott.

"[Our paper looks at] not just the temperatures but also the reducing Arctic sea ice and it includes changing rainfall patterns and it includes the fact that the atmosphere is getting more humid.

"And all these different aspects of the climate system are adding up to a picture of the effects of a human influence on our climate."

The Met Office study said that it was harder to find a firm link between climate change and individual extreme weather conditions - even though models predicted that extreme events were more likely.

According to the report: "Extremes pose a particular challenge, since rare events are by definition, poorly sampled in the historical record and many challenges remain for robustly attributing regional changes in extreme events such as droughts, floods and hurricanes."

Etched ostrich eggs illustrate human sophisticationEtched ostrich eggs illustrate human sophistication

Inscribed ostrich shell fragments found in South Africa are among the earliest examples of the use of symbolism by modern humans, scientists say.

The etched shells from Diepkloof Rock Shelter in Western Cape have been dated to about 60,000 years ago.

Details are reported in the Proceedings of the National Academy of Sciences.

The researchers, who have investigated the material since 1999, argue that the markings are almost certainly a form of messaging - of graphic communication.

"The motif is two parallel lines, which we suppose were circular, but we do not have a complete refit of the eggs," explained Dr Pierre-Jean Texier from the University of Bordeaux, Talence, France."The lines are crossed at right angles or oblique angles by hatching. By the repetition of this motif, early humans were trying to communicate something. Perhaps they were trying to express the identity of the individual or the group," he told.

Symbolic thought - the ability to let one thing represent another - was a giant leap in human evolution, and sets our species apart from the rest of the animal world.

Understanding when and where this behaviour first emerged is a key quest for scientists studying human origins.

Arguably the earliest examples of conceptual thought are the pieces of shell jewellery discovered at Skhul Cave in Israel and from Oued Djebbana in Algeria. These artefacts are 90,000-100,000 years old.

Shell beading from 75,000 years ago is also found at Blombos Cave in South Africa, as well as a number of ochre blocks that have engravings not dissimilar to those at Diepkloof.However, the significance of the Diepkloof finds may lie in their number, which proves such markings could not have been simple doodlings.

"What is extraordinary at Diepkloof is that we have close to 300 pieces of such engravings, which is why we are speaking of a system of symbolic representation," Dr Texier said.

The team, which includes Dr Guillaume Porraz from the University of Tubingen, tried themselves to recreate the markings using pieces of flint.

"Ostrich egg shells are quite hard. Doing such engravings is not so easy. You have to pass through the outer layer to get through the middle layer," Dr Texier explained.

The team's experiments also suggest that the colouration of the fragments is natural and not the result of the application of pigments.

The group was able to reproduce similar hues by baking pieces of shell near a fire. Professor Chris Stringer, of London's Natural History Museum, said the find was important.

"Here we've got something that we can compare with later material that clearly does have important signalling value in the populations," he.

"It's a very nice link between the Middle Stone Age, the later Stone Age and even recent population in South Africa. One question now is whether this is a special site, or as we excavate more sites will we find this material is more widespread?"