Has climate change arrived?

WASHINGTON - Is it just freakish weather or something more? Climate scientists suggest that if you want a glimpse of some of the worst of global warming, take a look at U.S. weather in recent weeks.

Horrendous wildfires. Oppressive heat waves. Devastating droughts. Flooding from giant deluges. And a powerful freak wind storm called a derecho.

These are the kinds of extremes experts have predicted will come with climate change, although it's far too early to say that is the cause. Nor will they say global warming is the reason 3,215 daily high temperature records were set in June.

Scientifically linking individual weather events to climate change takes intensive study, complicated mathematics, computer models, and lots of time. Sometimes, it isn't caused by global warming. Weather is always variable; freak things happen.

And this weather has been local. Europe, Asia, and Africa aren't having similar disasters now, although they have had their own extreme events in recent years.

But since at least 1988, climate scientists have warned that climate change would bring, in general, increased heat waves, more droughts, more sudden downpours, more widespread wildfires, and worsening storms. In the United States, those extremes are happening here and now.

"This is what global warming looks like at the regional or personal level," said Jonathan Overpeck, professor of geosciences and atmospheric sciences at the University of Arizona. "The extra heat increases the odds of worse heat waves, droughts, storms, and wildfire. This is certainly what I and many other climate scientists have been warning about."

Kevin Trenberth, head of climate analysis at the National Center for Atmospheric Research in fire-charred Colorado, said these were the very record-breaking conditions he has said would happen, but many people wouldn't listen. So it's I told-you-so time, he said.

As recently as March, a special report an extreme events and disasters by the Nobel Prize-winning Intergovernmental Panel on Climate Change warned of "unprecedented extreme weather and climate events." Its lead author, Chris Field of the Carnegie Institution and Stanford University, said, "It's really dramatic how many of the patterns that we've talked about as the expression of the extremes are hitting the U.S. right now."

"What we're seeing really is a window into what global warming really looks like," said Michael Oppenheimer, a Princeton University geosciences and international-affairs professor. "It looks like heat. It looks like fires. It looks like this kind of environmental disasters."

Oppenheimer said that before the East Coast was hit with triple-digit temperatures and before a derecho - a large, powerful, and long-lasting straight-line wind storm - blew from Chicago to Washington and pounded the Jersey Shore. The storm and its aftermath killed more than 20 people and left millions without electricity. Experts say it had energy readings five times that of normal thunderstorms.

Fueled by the record-high heat, this was among the strongest of this type of storm in the region in recent history, said research meteorologist Harold Brooks of the National Severe Storm Laboratory in Norman, Okla. Scientists expect "non-tornadic wind events" like this one and other thunderstorms to increase with climate change because of the heat and instability, he said.

Such patterns haven't happened only in the last week or two. The spring and winter in the United States were the warmest on record and among the least snowy, setting the stage for the weather extremes to come, scientists say.

"In the future," said climate monitoring chief Derek Arndt of the National Oceanic and Atmospheric Administration, "you would expect larger, longer, more intense heat waves, and we've seen that in the last few summers."

While at least 15 climate scientists told the Associated Press that this long, hot U.S. summer was consistent with what would be expected in global warming, history is full of such extremes, said John Christy at the University of Alabama in Huntsville. He's a global-warming skeptic who says, "The guilty party in my view is Mother Nature."

But the vast majority of climate scientists, such as Jerry Meehl, a climate extreme expert at the National Center for Atmospheric Research, disagree: "This is what global warming is like, and we'll see more of this as we go into the future."