Periods of the earth's warming are associated with an increase in biodiversity, according to a study published this week in the Proceedings of the National Academy of Sciences. While this may sound like good news, the timescales involved cancel out any benefits they might experience from the rising temperatures.

The team behind the study, led by Dr Peter Mayhew at York University, examined the earth's geological history and fossil records using improved data sets that looked at patterns of marine invertebrate biodiversity over the last 540m years.

They found that biodiversity increases over periods of warming in the earth's climate with many new species emerging, although these are simultaneously accompanied by extinctions of existing species.

Mayhew said: "What seems to be happening is that when we get a warming, this coincides with an upward shift in biodiversity in groups of organisms. So it looks like warm periods are boosting the generation of new species and that's improving biodiversity. However a bit later, and when I say 'a bit', I mean several millions of years later, you get extinctions occurring."

"It's a kind of a mixed picture," he added." We get an improvement in diversity but we also get extinction in new groups. It's just that overall the origination tends to out-do the extinction so biodiversity improves, generally."

But Mayhew doesn't think this changes what we currently understand concerning the loss of species as a result of today's man-made global warming.

"I don't think that there is any good news here", says Mayhew. "If what we need for diversity to improve in these warm climates is time for those organisms to evolve, then that time is going to be much longer than the lifetime of the human race. The lifetime of a species tends to be 1-10m years in the record. So that's how long we can expect humans maybe to survive ... if we get a fair chance at life.

"But I'm afraid it's not good news in terms of what we might experience from global warming in the next few decades. Because obviously extinction can happen rapidly, but speciation [the generation of new species] can't happen rapidly. So unfortunately we're quite likely, simply because of the rate of climate change today, to see extinctions occurring. And we're unlikely to see the benefits that might go along with that, which is the generation of new species."

Therefore despite of the possibility that climate change sceptics might takes these latest findings to suggest that the current warming of the planet is a good thing, Mayhew is very clear about what should be taken away from this study.

"Probably warming is good for speciation. In fact there are a lot of ecological studies that have suggested that there is the potential for earth to support biodiversity may in fact be greater under a global warming scenario. The difficulty is that potential doesn't necessarily translate into reality and species have to exist in order to fulfil that potential.

"I follow the scientific consensus here. The scientific consensus is definitely that current global warming is going to lead to a loss of biodiversity and potentially quite a significant loss. I don't think there is any good data to say otherwise at the moment and most of the data we have is strongly in that direction." He pointed out, for example, that there are big concerns about what is happening in the coral reefs.

So while the study does give us an insight into what happened to species when the planet warmed millions of years ago, it doesn't contradict predictions of greater species extinctions due to current rates of climate change.

Their findings contradict a previous study his team did in 2008 which found the opposite result: that biodiversity decreases when temperatures rise.

Mayhew explained: "Since 2008 new and better data and better techniques have come along which have enabled us to get a better picture of what's going on. And essentially the new data are different in that they take an ecological approach to sampling. They sample the fossil record like an ecologist today would sample a rainforest. In the past we haven't been able to do that properly."