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

Did you feel a small tremor rumbling underground last fall? Seismometers as far west as Seattle lit up on October 30. But the source of the recorded energy didn’t come from an earthquake. It came from Superstorm Sandy, an extreme hurricane that hit the East Coast thousands of miles away. What the…?

At the recent Seismological Society of America’s annual meeting, researchers presented their findings on seismic waves that are triggered by large storms and sometimes cause the ground at great distances to shake.

In the case of Sandy, the shaking was partly caused by the actual waves hitting the mid-Atlantic coastline. Of greater consequence were the waves colliding with other waves in the ocean, setting up a pattern of “standing waves” that reach the seafloor and transmit their energy. That force becomes seismic waves that travel through the crust and upper mantle under North America.

“They are not earthquakes; they are seismic waves,” says Keith Koper, director of the University of Utah Seismograph Stations. “Seismic waves can be created by a range of causes. We have beautiful seismic records of the meteor that hit Russia. That’s not an earthquake, but it created ground motion.”

Earthquakes, storms, and meteors are only three causes of seismic waves. Seismic activity can also occur from mining, traffic, construction, and even elephants communicating.

At the same meeting, researchers presented findings that Hurricane Irene may have caused aftershocks to a 5.8 magnitude earthquake in Virginia in 2011.

This isn’t the first time large storms have been linked to seismic waves, Koper adds. “Hurricane Katrina in 2005 was recorded by a seismic array in California, and they could track the path of the storm remotely using seismometers.”

Image: Keith Koper, University of Utah Seismograph Stations

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

For scientists, policy-makers and organizers who frequently discuss climate change, the last few years have been rough! While they still may be discussing it amongst themselves, with the economic downturn, a larger audience has been absent. An episode of Frontline explores the massive shift in public opinion on climate change.

But the last two weeks might change all of that.

Hurricane Sandy affected so many people that climate change popped up in many new conversations. Click on these questions to find some of these headlines:

• Was the storm caused by climate change?
• Are humans to blame?
• Will global warming bring more “frankenstorms” like Sandy?
• How can cities protect themselves?
• What are some of the financial impacts?
• How can communities adapt to a new normal of storms like these?
• How do we find stormproof solutions?

Will Obama’s second term allow him to speak more freely (and more urgently) about climate change? Scientific American says that we’ll likely only see “more of the same.” But New Scientist has some suggestions about how he can create a “climate change legacy.” And Brandon Keim, in Wired, sees opportunity for the President:

A cap-and-trade system for carbon pollution is unlikely, but other approaches are possible, from adapting infrastructure and improving post-disaster resilience to revenue-neutral carbon taxes and reduced fossil fuel subsidies.

Let’s hope these conversations start quickly (the Academy’s Peter Roopnarine blogs about climate change, providing many conversation starters). According to recent news headlines (here and here), we’re quickly looking at worst-case scenarios for global warming.

What do you want to say about climate change? Share below.

Image: NOAA