This is the third installment of a five-part series by Bill Chameides on How We Know Humans Cause Global Warming.

1. A 175-year-old Puzzle
2. What Chemistry Tells Us
3. Causes of Past Climate Change
4. The Medieval Warming Period
5. The Only Explanation Left

An argument I hear frequently from climate change skeptics goes like this: "Climate has undergone warming and cooling cycles for millennia. This is no different. It's just another naturally occurring warm cycle."

It's true that climate has undergone warming and cooling cycles for millennia, but it's not true that this is just another naturally occurring warm cycle. Here's why.

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The author of today's article, Mark MacLeod, is Director of Special Projects for our national climate campaign.

What do you get when a longtime champion of the environment and a respected Republican voice on both the economy and national security join forces in the Senate to write a climate change bill? A real opportunity for bipartisan action on global warming.

On Wednesday, Connecticut Independent Joe Lieberman and Virginia Republican John Warner announced a groundbreaking commitment to develop a comprehensive greenhouse gas cap and trade bill. They intend to bring it to a vote in their panel on the Senate Environment and Public Works Committee before the end of July.

A pile of climate bills have already been introduced in the Congress this year - why is this announcement such big news?

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The author of today's article, Annie Petsonk, is International Counsel at Environmental Defense.

When European countries ratified the Kyoto Protocol, they pledged to reduce their greenhouse gas emissions. To prepare, they designed the European Union Emissions Trading Scheme (EU-ETS), now the world's largest greenhouse gas cap-and-trade system.

Since the launch of the EU-ETS in January 2005, allowance prices have been volatile and are currently hovering around zero.

Click on graph to enlarge.

Many people point to these figures and proclaim the EU-ETS a failure. Here's why they're wrong.

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The author of today's article, Derek Walker, is deputy director of the state climate initiative at Environmental Defense.

Last week, New Jersey's House and Senate Budget Committees passed a landmark global warming bill called the "Global Warming Response Act". It sailed through the full House and Senate two days later and Governor Jon Corzine says he will sign it in July.

The bill will cap greenhouse gas emissions at 1990 levels by 2020, and lower the cap to 80 percent below current levels by 2050 (see New York Times article). It is the first bill in the nation to legislate a 2050 target. This is important because 2050 targets are crucial to avoiding the global warming tipping point, and are a component of the bills currently before Congress. When forward-looking states pass legislation like this, it can force the federal government to do likewise.

I went to Trenton to testify before the Budget Committee, and left there inspired.

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Three stories caught my eye this week. The first study adjusts earlier estimates of carbon uptake by land plants. In the other two articles, scientists document the biological effects of Europe's record-breaking temperatures, and estimate the risk of severe Mediterranean heat waves due to global warming.

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This is the second installment of a five-part series by Bill Chameides on How We Know Humans Cause Global Warming.

1. A 175-year-old Puzzle
2. What Chemistry Tells Us
3. Causes of Past Climate Change
4. The Medieval Warming Period
5. The Only Explanation Left

There's no question that carbon dioxide (CO₂) is a greenhouse gas that warms the planet, and that CO₂ has been increasing. The graph below shows it vividly (the measurements were taken at Mauna Loa, Hawaii).

But how do we know that the increase is due to people burning fossil fuels? One way is by analyzing the chemistry of our atmosphere, since human activities leave an unmistakable "fingerprint".

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The author of today's article, Sheryl Canter, is an Online Writer and Editorial Manager at Environmental Defense.

In poking around the blogosphere recently, I found several references to a Popular Mechanics article about something called an "Air Car". Air Car?? What I read left me with some questions, so I found the inventor's Web site and did some further reading.

It sounds like science fiction, but it's true. A car that runs on air - compressed air - will be sold in India starting in August 2008. It's designed mainly for city driving, and produces zero carbon emissions.*

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Today's guest blogger, Tony Kreindler, is a Media Director at Environmental Defense.

There's been a lot of buzz lately about the Energy Bill under debate in the Senate. With all the lobbying and spin, it can be hard to sort out what's really going on. Here's the bottom line.

When it comes to solving climate change, our best yardstick for measuring success is how much we cut global warming pollution. The Energy Bill could make some progress, but it's no substitute for the comprehensive climate legislation Congress will work on later this year. Let's look at the numbers.

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The RealClimate blog has great information on the science behind global warming. Recently they posted a resource page with links about climate change. They plan to update the page as they discover new resources, so you might want to bookmark it.

This is the first installment of a five-part series by Bill Chameides on How We Know Humans Cause Global Warming.

1. A 175-year-old Puzzle
2. What Chemistry Tells Us
3. Causes of Past Climate Change
4. The Medieval Warming Period
5. The Only Explanation Left

Most people these days accept that our planet is warming, but some find it hard to believe that mere humans could cause such a large-scale global change. How do we know that the warming is due to human activity? How can we be so sure?

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