# Highest CO<sub>2</sub> and Methane in 800,000 Years

*Published:* 2008-05-19
*Author:* Lisa Moore

![Lisa Moore](https://blogs.edf.org/climate411/wp-content/blogs.dir/7/files/2008/04/lisa_moore.jpg)*This post is by [Lisa Moore, Ph.D.](http://www.environmentaldefense.org/page.cfm?tagID=404), a scientist in the Climate and Air program at Environmental Defense Fund.*

In [IPCC](http://www.ipcc.ch/)‘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.

The research, published in *[Nature](http://www.nature.com/nature/journal/v453/n7193/edsumm/e080515-01.html)*, analyzes the atmospheric gases trapped in ice cores extracted from Antarctica. These ice cores are the oldest yet studied. In 2001, the 420,000-year old Vostok ice core from eastern Antarctica set the benchmark. In 2005, scientists analyzed a 650,000-year record from Antarctica’s Dome C. Now, drilling even deeper, scientists at Dome C have assembled an 800,000 year record of CO2, methane and temperature.

These are the main findings:

- CO2 and methane levels are higher today than they have been in at least the past 800,000 years.
- The strong correlations of methane and CO2 with temperature reconstructions are consistent back 800,000 years.
- The long-term cyclic changes in temperature, methane and CO2 that follow slow changes in Earth’s orbit are consistent back 800,000 years.

![Ice Core Record - 800,000 years](https://blogs.edf.org/climate411/wp-content/blogs.dir/7/files/2008/05/ice_core_record_800000_years.jpg)  
*CO2 (red) is in parts-per-million (ppm); methane (green) is in parts-per-billion (ppb); temperature (black) is relative to the average of the past millennium. [Reprinted by permission from Macmillan Publishers Ltd: Nature. "Windows on the greenhouse" by Ed Brook, Nature 453: 291-292, copyright 2008.](http://www.nature.com/nature/index.html)*

There are no surprises in the big picture, but more detailed analysis raises some intriguing questions. For example:

- Cold phases remain roughly similar throughout the 800,000 year record, but starting about 450,000 years ago, warm phases got warmer. Why?
- What accounts for the unusually low value for CO2 (172 ppm) about 667,000 years ago?

Scientists are already forming hypotheses about these and other questions. To help find answers, scientists have launched a new project to obtain a [1.5 million year record](http://www.ipy.org/index.php?/ipy/detail/ipics_ipy). That will mean drilling in locations with older ice because they’ve nearly reached bedrock at [Dome C](http://www.climate.unibe.ch/?L1=research&L2=rice).

In the meantime, one thing is clear: Human activity has had an enormous effect on Earth’s natural cycle. It’s time to take responsibility for the damage we’ve caused and cap emissions.