Each spring, dormant plants awaken and begin taking in CO2 to fuel photosynthesis.

Boreal forests in particular have shown marked increases in carbon uptake during summer.

Ecosystem productivity is rising at high latitudes, with a roughly 50% increase in the amount of carbon cycling through northern landscapes since the 1950s, according to an analysis of atmospherics carbon dioxide trends published today in Science.

Northern forests are not just surviving but thriving.

says study coauthor Ralph Keeling, a geochemist at the Scripps Institution of Oceanography in La Jolla, California, which runs a CO2 monitoring programme at Hawaii's Mauna Loa Observatory.

"Something quite massive is taking place on large parts of the landscape that are not directly impacted by humans,"

The pendulum reverses in autumn, when the release of CO2 increases as leaves fall and photosynthesis gives way to respiration by plants and microbes.

The research examines large seasonal swings in atmospheric CO2 levels in the Northern Hemisphere, which is home to the bulk of Earth's land.

"Everybody hears about negative feedbacks on the carbon cycle, but this study shows that the activity of the biosphere is increasing in spite of climate change."

The results suggest that the amplitude of the annual C02 swing has increased over time and continues to rise today, despite growing concerns about the vulnerability of northern forests to pests and fires.

Researchers compared detailed aerial measurements of atmospheric CO2 levels taken in 2009-11 with data from an aerial survey conducted in 1958-61 and observations from Mauna Loa and a second long term monitoring site in Barrow, Alaska.

says Philippe Ciais, a carboncycle researcher at the Laboratory of Climate and Environmental Sciences at Gif-sur-Yvette, France, who was not ivolved in the research.