When this concentration rose above 13%, wildfires became possible.

In closed environments, the concentration of carbon monoxide can easily rise to lethal levels.

As a general trend, the concentration of oxygen in the atmosphere has risen gradually over about the last 2.5 billion years.

There also appears to be general agreement that atmospheric concentrations of greenhouse gases are rising.

However, nitrate concentrations in the lake have been continuously rising for more than a century.

During that span concentrations never rose above 280 parts per million.

In the simulation, the atmospheric concentration of carbon dioxide rises about 0.45 percent a year through 2300.

If the bottom two merged, concentration would rise 11 percent.

As this increase amounted to 50%, the relative concentration of involved genes rose from 20 to 30%.

Similarly, concentrations in the atmosphere are not only at a new record, but are rising faster than ever.