This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

In 1992, the world's nations gathered to negotiate the United Nations Framework Convention on Climate Change. The 192 nations that ratified this treaty - including the U.S. - agreed to the following objective:

[T]o … prevent dangerous anthropogenic interference with the climate system… within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner.

The definition of "dangerous" is a social and political judgment that is informed by science. But even if we all agreed on which outcomes we wanted to avoid, scientists couldn't say precisely how much we have to cut emissions to achieve these outcomes. We have good best estimates, but there's always a degree of scientific uncertainty.

Here's why.

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This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

IPCC scientists have been saying for years that man-made global warming is likely to increase extreme weather events. A new report ("Weather and Climate Extremes in a Changing Climate") from U.S. government scientists confirms these findings, and focuses specifically on the U.S.

It's certainly timely, considering the devastating floods in the Midwest.

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This post is by James Wang, Ph.D., a climate scientist at Environmental Defense.

The record floodwaters in Iowa and other parts of the Midwest are claiming lives, destroying homes and crops, contaminating drinking water, and - as the AP puts it - spreading "a noxious brew of sewage, farm chemicals, and fuel that could sicken anyone who wades in." The cost in human anguish is incalculable.

But why is it happening? Is it just a freak of nature? One causal element, as reported in today's Washington Post, may be human reengineering of the landscape. Mary Kelly, who heads up EDF's rivers and deltas program, gives a good overview of these issues.

Another element may be global warming, which increases the probability of extreme weather events like torrential rain.

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This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

In IPCC's Third Assessment Report (2001), scientists reported that carbon dioxide (CO₂) and methane levels were higher than at any time in the past 420,000 years. In their latest report (2007), IPCC scientists raised the number to 650,000 years.

Last week, scientists again revised the number upward. New research shows that CO₂ and methane levels are higher today than they have been in at least 800,000 years.

Here's how they know.

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This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

An article in this week's Nature predicts that Europe and North America will cool slightly over the next decade. No, this doesn't mean that global warming has stopped.

The new paper describes a climate model that makes short-term (decadal) predictions based on ocean dynamics. The decade-long cooling is just a temporary offset to warming from human activity. After it passes, temperatures will begin climbing again. By 2030, the model forecasts the same global temperatures as the IPCC.

This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

Last week, NOAA released some disheartening numbers: both CO₂ and methane increased sharply last year. Growth rates are increasing (see graph to the right).

The CO₂ numbers weren't a surprise. A paper with similar findings was published last November by a team that included a NOAA scientist. I wrote a blog post summarizing the study, which analyzed the reasons behind the trend (see Rise of Atmospheric Carbon is Accelerating).

The methane numbers, however, were disturbing. Until this year, methane levels have been essentially unchanged since 1998.

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This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

There's an email making the rounds lately - an invitation to take a Global Warming Test. It starts off reasonably enough (yes, global warming is real), but then quickly devolves into ridiculousness - ridiculousness presented in a way that looks misleadingly "scientific".

For those interested in truth, here are the real answers to the Global Warming Test.

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This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense Fund.

According to NOAA's National Climatic Data Center, this past winter was the coolest since 2001. A single season can't determine a long-term trend any more than a single month can (see my previous post, "Did Global Warming Stop in January?"). But the recent cooler temperatures do offer an opportunity to talk about La Niña - a climate pattern that causes short-term cooling.

This winter's La Niña is the strongest (coldest) since 1989, so we'd expect the weather to be cooler than usual. But even so, the cooling didn't come close to offsetting the warming of the past 50-100 years. As you can see in the graph below, the cooling barely takes us back to 2001.

Data source: NASA. Each dot is a three-month period (season).

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This post is by Sheryl Canter, an Online Writer and Editorial Manager at the Environmental Defense Fund.

On Monday, the Washington Post reported that new studies say carbon output must be near zero to avert danger. They referred to two recent studies, one published in Geophysical Research Letters and one in the journal Global Biogeochemical Cycles.

I asked the scientists here at EDF about this. It turns out what's missing from the Washington Post article is the time frame. Yes, we have to bring emissions to near zero, but it doesn't have to be tomorrow. And moreover, this isn't news!

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This post is by Lisa Moore, Ph.D., a scientist in the Climate and Air program at Environmental Defense.

January 2008 was the coldest month in several years, according to the scientific groups that track global temperature. Is it true, as DailyTech concludes, that January's cold "wipes out a century of warming"? Has global warming stopped?

In a word, no. A single month does not make for a climate trend. Let's look at the data.

Source: Raw data from the U.K.'s Met Office Hadley Centre (see description of data).

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