When are extreme events part of natural climate variability and when are they due to climate change? It’s important to ask—no matter where you stand on the role of humanity’s impact on the environment.

A group of international scientists decided to address this question, focusing on a dozen or so extreme events from 2012. Their results were published last week in the Bulletin of the American Meteorological Society. (The findings are also available in a downloadable report.)

And the results, were, well, variable.

The researchers did not look at Hurricane Sandy, but they did examine the flooding and the inundation it caused. Because of sea-level rise (a direct result of climate change), the researchers determined that the superstorm did far greater damage than it would have with oceans at normal levels.

The team also determined that heavy rains in the United Kingdom, Japan, and China were not due to global warming, and Australia’s above-average rainfall was due to a La Niña event (or short-term climate variability).

However, a deluge in New Zealand was due to climate change. From Wired:

Total moisture available for this extreme event was 1% to 5% higher as a result of anthropogenic greenhouse gas emissions.

And Arctic sea ice melt? The cap of sea ice covering the North Pole shrunk to its smallest extent last summer. The cause? Climate change.

What about last year’s devastating drought in the Midwest? Scientists judged that climate variability was to blame—not global warming.

However, Stanford researchers did find that the extreme heat that came with last summer’s drought could be attributed to climate change. They also found strong evidence that the high levels of greenhouse gases now in the atmosphere have increased the likelihood of severe heat.

In addition, their findings indicate that extreme weather in the north-central and northeastern United States is more than four times as likely to occur than it was in the pre-industrial era.

The Palo Alto scientists hope the results from these studies can help to quantify the true cost of emissions to society, since the cost of the disaster is measurable.

“Knowing how much our emissions have changed the likelihood of this kind of severe heat event can help us to minimize the impacts of the next heat wave, and to determine the value of avoiding further changes in climate,” says lead author Noah Diffenbaugh, a Stanford associate professor of environmental Earth system science.

Image: Theresa L Wysocki/Flickr

How will climate change affect different species? Will organisms be able to adapt quickly enough to survive in a rapidly changing environment?

Researchers at the University of Oxford are attempting to predict this with small, short-lived birds like the great tit (Parus major). In a study published this week in PLoS Biology, the scientists discovered that great tits living in a forest near Oxford have been able to survive and adapt to a 1°C temperature increase over the past 50 years.

After analyzing those 50-plus years of data collected on the birds in their habitats, the authors studied when the birds lay their eggs relative to spring temperatures, as well as how the birds have tracked the shifts in peak caterpillar numbers caused by the changes in temperature. They found that the birds are now laying their eggs an average of two weeks earlier than they did 50 years ago, primarily as a result of phenotypic plasticity.

Phenotypic plasticity enables organisms to adjust their behavior rapidly in response to short-term changes in the environment. Jack Dumbacher, curator and department chair of Ornithology & Mammalogy here at the Academy, explains, “It’s heritable but it’s not an evolutionary, or genotypic change. There’s no change in the genes.”

The authors’ predictions show that phenotypic plasticity could allow the great tits—and similar birds—to survive warming of 0.5°C per year, easily outpacing the current worst-case scenario of 0.03°C from climate models.

Dumbacher says that while this study is interesting and a good reminder how adaptable one species may be, he emphasizes that temperature increase is just one effect of climate change. Temperature variance and extreme weather are other effects with unknown results to various ecosystems, he says. In addition, Dumbacher reminds us that the great tits and caterpillars play roles in a much larger ecosystem, where the web of relationships is so interdependent that one small change to one small organism in that web could easily affect other species.

One effect of climate change that Dumbacher stresses (and the study does not mention) is invasive species. As temperatures change, habitat ranges change for different species, which can result in one species invading the habitat of another. One example Dumbacher gives is the Northern Spotted Owl (Strix occidentalis caurina). These birds have been able to adapt to a 1°C temperature increase over the past 100 years but are now facing a fierce competitor in the Barred Owl (Strix varia), an eastern species that now finds itself in the same territory as the Northern Spotted Owl.

“Climate change is more than a one degree temperature increase,” Jack says. “And while a species may demonstrate plasticity within different temperature regimes, it’s likely that ecosystems are not as adaptable. This why climatologists have such a difficult time predicting the effect of climate change on organisms.”

Image: Luc Viatour/Wikipedia