However, over the next 100 years, methane concentrations are likely to rise.

Data from 2007 suggested methane concentrations were beginning to rise again.

Methane concentrations have more than doubled in the past 100 years.

Atmospheric methane concentrations have increased by 150% during the past 200 years.

At the same time methane concentrations also rose rapidly, the agency said.

Methane concentrations may vary somewhat by region and over time.

By 1983, several instruments for measuring methane concentration in air had been developed.

She said there had been no sign of increased methane concentration prior to the blast.

First thing, work out what the real methane concentrations must be to account for Louie's data.

Average methane concentrations in the Arctic currently stand at around 1.85 parts per million, which is a record for the last 400,000 years.

Since the 1800s, atmospheric methane concentrations have increased annually at a rate of about 0.9%.

In mines, giant fans are used to keep methane concentrations below certain levels.

So changes in carbon dioxide or methane concentrations would have a relatively small impact.

However, during the 1990s, methane concentrations barely increased at all (see Fig.

Methane concentrations in the atmosphere have been measured continuously since 1978.

Today, outside air is continuously pumped through a mine to keep methane concentrations below 1 percent.

"When the methane concentrations are that high, the water can bubble like champagne," Jackson said.

Methane concentrations were calculated as the difference between breath and a corresponding room air sample.

Current methane concentrations in the Arctic are the highest in 400,000 years.

The number of stations monitoring atmospheric methane concentrations worldwide is very few.

But this is the first time that scientists have found a sustained plateau in methane concentrations, from 1999 to 2002.

Methane concentrations are approximately double the pre-industrial levels (Figure 2).

These values should be averaged to give the daily mean methane concentration ( ).

Such instruments require oxygen to work and can be inaccurate if methane concentration is very high.

Despite uncertainties about such changes, experts expect atmospheric methane concentrations to continue to rise for at least the next 50 years.