Forests and Climate Change
Forests play a major role in Earth’s carbon cycle. Trees convert
atmospheric carbon from CO2 into organic woody
biomass as part of a respiratory process called photosynthesis.
Trees then store the carbon until the woody biomass is destroyed.
This carbon storage is called sequestration.
When forests are cut down, not only does photosynthesis– and
thus carbon absorption– cease, but also the carbon stored
in the wood of the trees is released into the atmosphere as CO2
if the wood is burned or decays.
Overall, forest ecosystems store between 20 and 100 times more carbon
per unit area than do croplands.
Deforestation is an important factor in global climate change, as
well as a root cause of worldwide loss of biodiversity, and of diminished
water quality and quantity worldwide.
Deforestation and changes in land use play a significant role in global
climate change because carbon dioxide is released into the atmosphere
when forests or forest products are burned. If the forest is converted
to other uses such as agriculture, future carbon sequestration is
lost as well.
According to the IPCC, 1.6 billion
tons of carbon dioxide a year are released to the atmosphere due to
deforestation (cutting and burning of forests).
forests burn, stored carbon dioxide is released to the atmosphere.
Photo courtesy National Oceanic and Atmospheric Administration.
the early 1900s, deforestation was the dominant source of increased
CO2 in the atmosphere. Since that time, the
burning of fossil fuels has surpassed deforestation, but according
deforestation and forest degradation are estimated to be responsible
for up to 20 percent of the greenhouse effect.
vs. temperate deforestation:
deforestation first occurred in temperate zones as forest land was
converted for agricultural use. In the last 50 years, however, the
fastest rates of deforestation have taken place mostly in tropical
regions as impoverished nations have converted their land for farming
and grazing. Thus as important as temperate forests are in the carbon
cycle, most of the change worldwide currently is taking place in
Rates of tropical deforestation increased between 50 and 90 percent
in the 1980s, while the area of temperate forests– albeit
encompassing smaller second- or third-growth trees– has remained
constant or increased in the last 50 years. (This statistic does
not take into account the loss of biodiversity found in many temperate
"plantation" forests. In other words, the replacement
of an acre of older or larger trees with an acre of seedlings almost
always represents a major loss of habitat values, as well as aesthetics.)
temperate regions, forests primarily are cut for timber or paper.
While this has a devastating effect on forest-dependent species,
with regard to the carbon cycle most of the carbon still is stored
in the wood, regardless of the wood’s use. After a few decades,
however, most of this stored carbon is released when the wood or
paper is burned or decays
is often burned to clear it for agriculture. Photo courtesy
University of Leeds Dept. of Geography/RAINFOR
tropical forests, on the other hand, are cut for conversion to agricultural
use. The cheapest method of converting the land is the "slash-and-burn"
technique. Burning the biomass releases enormous amounts of CO2
into the atmosphere. Coupled with the loss of carbon-sequestering
material, this burning plays a major role in the greenhouse effect.
Subsequent land use may be the most important factor in determining
the full role played by deforestation in global warming. In temperate
areas conversion of land from forest to other uses essentially has
ceased. Again, this fact does not diminish the great environmental
harm done in replacing natural stands of larger trees with monocultures
tropical regions, however, conversion is occurring at a rapidly
increasing rate. A 1991 study shows 90 percent of deforested tropical
regions becoming farms or ranchland, while only 10 percent is replanted
for future timber harvests.
Scientists estimate that the largest loss of carbon from both biomass
and soil occurs with a change of land use from tropical forest to
permanent agriculture. Conversion of forest land to pasture causes
similar carbon loss, and the effective greenhouse gas emissions
are significantly higher when methane emissions from cattle grazing
are often cleared for cattle grazing. Photo courtesy the Bureau
of Land Management.
as Carbon Sinks
One point of contention in the negotiation of the Kyoto Protcol
has been whether to take the carbon-absorbing capacities of forest
lands into account in measuring a nation's carbon dioxide emissions.
are still unresolved questions about how to account for a gain or
loss of carbon-absorbing forest "sinks"—for example,
should harvesting timber count as part of a nation’s emissions
because of the resulting loss in carbon-absorbing forest? And should
re-planting deforested areas count as emissions "credits"?
While a forest can act as a carbon repository, the way that a forest
is managed can increase or decrease its capacity. Clearcutting not
only removes carbon-absorbing trees, but also allows the CO2
stored in the soil to escape. According to scientists at the University
of Alberta, letting trees grow longer before harvesting them
allows the soil to store more carbon. Thinning and fertilizing forests
may also increase their ability to store carbon.
Although the practice of giving a nation emissions credits for net
increases in forest stocks and taking away these credits for reduction
of these stocks might appear to be fair, the actual effect of forestry
activities on carbon dioxide emissions is extremely difficult to
monitor. There is significant concern that emissions credit trading
could result in a net gain in CO2 emissions.
of carbon by biomass is not a long-term solution. Undisturbed forests
reach an equilibrium after about 100 years, with the net absorption
of carbon roughly equaling the net emission.
A paper published bythe Pew Center for Global Climate Change, "Land
Use and Global Climate Change: Forests, Land Management, and the
Kyoto Protocol," points out that "increasing carbon
storage cannot by itself solve the problem of increasing atmospheric
CO2, but it can help, especially in the short
Forests Forever is opposed to emissions credit trading because we
believe it is unlikely to either reduce net carbon dioxide emissions
or promote sustainable forestry. Current approaches to carbon credit
trading raise significant concerns regarding environmental justice,
monitoring and enforceability, and the potential for abuse when
applied to major hydro projects. Emissions credit trading could
shift the onus for reducing atmospheric carbon onto those countries
least responsible for creating the problem and least equipped to
effect a solution.
Impacts of Climate Change on California
©2016 Forests Forever. All Rights Reserved.