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

Four amazing and passionate scientists discussed different aspects of our changing world—wildlife, drought, storms and the tree-ring record—at a press conference titled, “Did Climate Change Cause Superstorm Sandy?”

Remember, these are scientists, not politicians (see more in Andy Revkin’s New York Times blog). They need evidence to see causal effect between one event and another. And for these recent storms and weather patterns, there just isn’t enough evidence. Yet.

But are these researchers glad that these events are focusing Americans’ attention (including the President in his recent State of the Union address) on climate change? Most definitely. Yes.

Here’s what they do know. Climate change is affecting the probability of storms like Sandy and Nemo. There is evidence that in our warming world, severe storms will happen more frequently.

Researchers understand that global warming and other human-related activities are affecting where animals live, move and mate, and when plants bloom.

Scientists also know that temperature increase is one factor in drought. Texas temperatures have risen steeply in just the past 15 years and drought has increased.  And now Texans are talking about climate change, said John Nielsen-Gammon of Texas A&M University. The drought alone didn’t alarm them about climate change, but the decreased water supply has made people and politicians alike take notice.

And the speakers are hopeful and passionate that we’ll start doing something about these effects—reducing fuel emissions, restoring habitats, becoming more aware of climate change.

What do you know and feel? Share with us here.

Midwest drought image: cwwycoff1/Wikipedia

What we call Asian carp here in the US are actually four species of fish, according to the USDA: the Bighead carp, black carp, grass carp and silver carp. They were originally brought to the US to do good. According to NPR:

Originally imported to help control algae in fish farms and water treatment plants in the South, Asian carp made their way into Louisiana rivers, possibly during floods in the early 1990s, and spread quickly up the Mississippi River and its tributaries.

Lake Michigan is connected to the Mississippi by a series of artificial locks that bring commercial ships into and out of the Great Lakes and specifically the Chicago area. Barriers have been built to keep carp out, but recently, one of these invaders was found past the barrier, in Lake Cascade, six miles south of Lake Michigan. The New York Times quoted Henry Henderson of the Natural Resources Defense Council reacting to the news:

Asian carp are like cockroaches; when you see one, you know it’s accompanied by many more you don’t see.

Why the barriers? Are Asian carp so bad? Well, here’s what Time has to say:

They can weigh up to 100 pounds and measure up to 20 feet, and eat 40 percent of their weight daily in plankton, thus knocking out the bottom of food chains. Even crazier, they launch themselves out of the water when startled, often hitting — and injuring — boaters.

It’s hard to say if these fish will cause problems for the native species in the Great Lakes, according to the Academy’s Peter Roopnarine, PhD. He does a lot of work with food webs that include both native and non-native species, and says that, “it’s not clear why some exotic species become established and some don’t.” For example, the San Francisco Bay has many invasive species, but none have yet to cause native species to go extinct.

That doesn’t stop the controversy, though. The Asian carp have swum right into the middle of one, with several groups taking sides. 80beats from Discover described it this way, earlier this year:

On one side, many environmentalists, as well as people who rely on Great Lakes fishing for their livelihood, have called on the federal government to shut down locks that connect the river to Lake Michigan…

…Naturally there’s one group that would be mighty upset at closing the shipping locks: shipping companies.

Earlier this month, the governor of Illinois, hoping to find a solution that won’t close the locks, announced a plan to open a fish processing plant and export the carp to China.

Then, this week, five states filed a lawsuit against the Metropolitan Water Reclamation District of Greater Chicago and the Army Corps of Engineers. Per AOL,

The lawsuit seeks an order to close Chicago shipping locks that provide a century-old pathway to the Great Lakes via the Mississippi River basin. The lawsuit was filed by Michigan, Wisconsin, Ohio, Minnesota and Pennsylvania.

Who expected a fishy tale could get this large? Those of us in northern California know it only too well— the state involvement, debates, lawsuits—sounds like the Delta smelt. Except, ironically, the smelt are native to this area and have to compete with larger, invasive fish.

What will be the next big fish to fry?

Creative Commons image by kate.gardiner