New Evidence on Earth and Within It Affirms Climate Change

The green and blue patches in this polar view of Earth represent increased plant growth.

Washington — Two research projects releasing data in early March provide new evidence that the Earth is warmer than it used to be. One group used satellite data to track the spread of plant life into higher latitudes than cold temperatures ever allowed in the past. Another group has examined ice and sediment cores gathered around the globe to calculate an unbroken record of temperatures over the past 11,300 years.

Examining satellite data from 1982 to 2011, a NASA-funded study found that the ground vegetation growing in 45 degrees north latitude to the Arctic Ocean looks more like what was found 4 to 6 degrees further south 30 years ago.

“It’s like Winnipeg, Manitoba, moving to Minneapolis–St. Paul in only 30 years,” said Compton Tucker of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, a co-author of the results published March 10 in Nature Climate Change.

Warming trends have extended the growing season, resulting in large patches of “vigorously productive vegetation” that span a third of the northern landscape, according to a NASA news release.

“Higher northern latitudes are getting warmer, Arctic sea ice and the duration of snow cover are diminishing, the growing season is getting longer and plants are growing more,” said Ranga Myneni of Boston University’s Department of Earth and Environment.

Over some 9 million square kilometers — an area roughly equal to the contiguous United States — the plant life covering the landscape above the 45th parallel north resembles the 1982 landscape 400 to 700 kilometers south.

What Myneni calls an “amplified greenhouse effect” is creating ecosystems that produce vegetation unlike any seen in the past. Increased concentrations of greenhouse gases trap Earth’s heat and prevent it from venting into space, creating warming on the planetary surface. Warming on the ground melts the polar sea ice and snow cover, which, consequently, creates darker oceans and landscapes, further multiplying the heating effect.

If changes similar to those of the last 30 years occur in the future, the result might be increasingly temperate ecosystems at higher latitudes, but that is not inevitable. Forest fires, pest infestations or summer drought could intervene to restrain the vegetation growth.

WHAT THE ICE BORES SHOW

A joint research project tapping ice and sediment cores at 73 locations around the world has allowed scientists to calculate temperatures more than 11 centuries in the past. The scientists from Oregon State University (OSU) and Harvard University find that the 21st-century planet is warmer than the globe has been during 70 to 80 percent of the last 11,300 years.

“This research shows that we’ve experienced almost the same range of temperature change since the beginning of the Industrial Revolution as over the previous 11,000 years of Earth history — but this change happened a lot more quickly,” said Candace Major, a program director at the National Science Foundation, the funding source for the work.

The history revealed through the ice and sediment borings shows that during the last 5,000 years, Earth cooled on average about .7 degrees Celsius until the last 100 years, when the evidence shows the planet warmed by the same amount.

Other researchers have produced climate forecasts that project warming temperatures could bring an increase of 1 to 6 degrees by the end of this century, largely due to increased carbon emissions.

“What is most troubling is that this warming will be significantly greater than at any time during the past 11,300 years,” said Peter Clark, an OSU paleoclimatologist and a co-author of this research.

The researchers used fossils from ocean sediment cores and terrestrial archives to reconstruct this 11-millennia temperature record. The chemical and physical characteristic of the fossils provide sufficient information for researchers to calculate corresponding temperatures during their lifetimes.

The slowness of temperature change over the first 11 millennia compared to the rapid change in the last 100 years leads the researchers to the conclusion that carbon emissions entering the atmosphere as a result of human activities caused the warming trend.