"We know the climate is warming. We know that humans are now in the driver’s seat of the climate system. We know that, over the next century, if nothing is done to rein in emissions, temperatures will likely increase enough to profoundly change the planet."

Those were the words of Andrew Dessler, climate scientist from Texas A&M University, as he addressed the U.S. Senate committee on environment and public works as part of a four-hour hearing on Thursday.

One of the expert witnesses on climate invited to testify, Dessler emphasized that global warming is a "clear and present danger." Dessler's testimony, which coalesced around four main points, warned:

1. The climate is warming. By this I mean by this that we are presently in the midst of an overall increase in the temperature of the lower atmosphere and ocean spanning many decades.

2. Most of the recent warming is extremely likely due to emissions of carbon dioxide and other greenhouse gases by human activities.

3. Future warming could be large. As a consequence of our understanding of the climate system, unchecked greenhouse-gas emissions would lead to warming over the 21st century of 4.7 - 8.6°F (for the global average).

4. The impacts of this are profound... The virtually certain impacts include increasing temperatures, more frequent extreme heat events, changes in the distribution of rainfall, rising seas, and the oceans becoming more acidic

The hearing, billed as a session to discuss President Obama's environmental policies, included voices of climate denial from within the committee. “I think we should be able to talk openly about climate science issues, such as the link between climate change and human activity,” said Mississippi Sen. Roger Wicker (R), implying that there is not an established linked.

This is despite the fact that scientists overwhelmingly agree that global warming over the past century is very likely caused by humans.

Dessler urged policy makers to heed the call of the scientific community and take immediate action to curb greenhouse gases.

"Time is not our friend in this problem," he urged. "By the time everyone agrees we have a problem, it is too late to do much about it."

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