Human Impact On Global Land
Surface Extensive Since 1700, UNH Scientist Reports
Contact: David Sims
Institute for the Study of Earth, Oceans, and Space
Sept. 23, 2005
Editors/reporters: George Hurtt may be reached at 603-498-3775.
DURHAM, N.H. – In a study led by University of New Hampshire
scientist George Hurtt, new global land-use history reconstructions
suggest that between 42 and 68 percent of the land surface has been
impacted by human land-use activity since the year 1700. These new
estimates are substantially larger and more comprehensive than previous
estimates. Moreover, because these estimates includes all ice-free
land surfaces, the estimated percent of land area impacted would
be much higher if nonproductive lands such as deserts were excluded.
“Humans have a big impact on a lot of different aspects of
the Earth system,” says Hurtt, assistant professor of natural
resources at the UNH Institute for the Study of Earth, Oceans, and
Space and the Department of Natural Resources. UNH co-authors of
the study include Berrien Moore, Stephen Frolking, and Matthew Fearon.
The study was also co-authored by Steve Pacala, Elena Shevliakova,
and Sergey Malysev of Princeton University, and Richard Houghton
of the Woods Hole Research Center.
Hurtt continues, “One type of impact is through our atmospheric
emissions while another is how we’re altering the land surface
through land-use activities” – the focus of this study.
Land-use activities affect many different things such as the structure
of ecosystems, distribution of species, the carbon cycle, water
cycle, and even the planet’s energy balance.
“This study is the first spatially resolved 300-year reconstruction
of how humans have impacted the land surface globally through land
conversions, for example, land clearing for agriculture, agriculture
abandonment, etc., and includes the first reconstruction of global
wood harvesting activity over that time period,” Hurtt says.
To produce the estimates, the study used data from remote sensing
satellites, historical statistics on land use, and other sources
of information in a massive computer simulation to estimate some
100 million potential historical land-use events globally.
One important outcome of this study is that it provides the first
global estimates of the spatial pattern and age of lands recovering
from prior land-use activities. Logging and the clearing of land
for agriculture releases carbon to the atmosphere. Similarly, allowing
forests to regrow from logging, and recover from the abandonment
of agriculture, creates areas that accumulate carbon in vegetation
and soils. This study provides the basis for the first global, spatially
resolved, estimates of carbon sources and sinks that result from
land-clearing and regrowth activities.
In previous studies, U.S. ecosystems have been shown to be a net
sink for carbon. The major factor responsible for the sink is the
contemporary regrowth of forests on land that was previously cleared
for agriculture. This new study provides the basis for analogous
estimates globally, and may ultimately lead to helping to solve
the “missing carbon sink” problem – the gap in
the global carbon budget between known sources and sinks of carbon
to the atmosphere.
Hurtt will give a “platform” presentation on this study
at the upcoming Seventh International Carbon Dioxide Conference
to be held September 25-30 in Boulder, Colorado. Testament to just
how important carbon science has become as climate change garners
more scientific interest, 500 carbon scientists, representing a
variety of disciplines including atmospheric chemistry, oceanography,
and terrestrial ecology, are expected to attend the conference.
The first carbon conference, held in Bern, Switzerland in 1981,
attracted 40 scientists.