Effects of Tropical Deforestation on Climate and Agriculture
Full paper available A policymaker summary for download at: of the article published in http://eorder.sheridan.com/3_0/display/index.php?flashprint=4415 Nature Climate Change Further questions, please contact: December 18, 2014 Dr. Deborah Lawrence, [email protected]
Flickr/Neil Palmer/CIAT Key messages Deforestation contributes Deforestation-induced to global warming, which in climatic changes interact turn creates future with global warming challenges for agriculture. caused by greenhouse gas emissions, each potentially having a worsening effect on the other. Models A new study in Nature suggest tipping points exist Climate Change provides after which impacts will powerful evidence that accelerate and forest loss, deforestation poses and therefore risks to additional threats to food agriculture, could become production and the climate. permanent. Deforestation creates immediate impacts on rainfall and temperature, which can occur locally and as far away as other continents. Deforestation creates new risks for agriculture…
Luiz E. O. C. Aragao, “Environmental science: The rainforest’s water pump,” Nature, Sep. 5, 2012.
Tropical forests move more Deforestation causes These impacts can affect water than any other increases in temperatures soil moisture, reducing ecosystem on land, turning and changes in the amount yields in some areas and soil water into moisture in and distribution of rainfall increasing flooding in the air, cooling the —generally creating a drier others. atmosphere above them. climate. Modeling low to high forest Deforestation can also …it can result loss outside protected affect the duration of the in acute local areas in the Amazon, one wet and dry season. study showed that: • In parts of the Amazon, the impacts… • Pasture productivity declines rainy season is delayed by by 28-33%, and cattle two weeks due to production may cease to be deforestation. viable in some areas • Deforested areas get • Soy yields drop by 25% in warmer, and the risk to over half the Amazon and by agriculture is especially great 60% in a third of the area. when higher temperatures correspond with periods and areas of decreased rainfall.
Flickr/Scott Bauer/USDA Flickr/Leonardo F. Freitas Temperature increases from deforestation can generate …and affect large upward-moving air masses. When these hit the food production upper atmosphere they cause ripples, similar to a tsunami. The exact impacts are highly uncertain, thousands of but models show: miles away.
• A 40% clearing of the • Complete deforestation of • Complete deforestation in Amazon will reduce rainfall Central Africa would likely Southeast Asia would over 2000 miles away in the cause declines in rainfall in increase rainfall in some Rio de la Plata agricultural the Gulf of Mexico and parts parts and decrease rainfall in basin. of the US Midwest and other parts of China and Northwest and increase it on India • Complete Amazon the Arabian Peninsula. deforestation would reduce Precipitation could also rainfall in the US Midwest, decline in Ukraine and Northwest and parts of the southern Europe south during the agricultural season
The three major forest Rainfall in the tropics tends Impacts of basins do not respond the to decrease with deforestation same; deforestation in the deforestation, but can vary Amazon and Central Africa depending on the scale, on rainfall are have stronger impacts on pattern and placement of warming and drying than in land clearing. For example: Southeast Asia, whose complex and • Deforestation in a monsoon dynamic can continuous block will lower uncertain counteract the effects. rainfall more than the same amount of forest clearing in distributed patches.
• Palm trees, soy crops and pasture all move water to air at different rates.
Partial deforestation leads to less severe impacts, but still affects temperature and rainfall. For example, business as usual deforestation of the Amazon leads to similar reductions in rainfall in western Amazon as complete deforestation, but has less impact in the eastern Amazon. The study shows that In Central Africa and A tipping point tipping points may exist. Southeast Asia, a sudden for deforestation For example, if forest loss reduces rainfall, deforestation reaches but gradual decline of 30-50% in the Amazon forest cover produced a basin, climate impacts modest increase in rainfall. could accelerate and As the size of a deforested forests could be replaced area increases, rainfall by savannahs. generally switches from a net increase to a net decrease within a given region. A TIPPING POINT At 30–50% deforestation, A much lower tipping point may exist if forest loss occurs climate impacts could accelerate in areas that are particularly important for the movement and forests could of atmospheric moisture. For example, small-scale be replaced with deforestation in coastal areas could disrupt the movement savannahs. of moisture from ocean to areas further inland. Conclusions This is a rapidly evolving field. Much of what we know has only been learned in the past 10 years, but tells us that:
• Tropical deforestation • Avoiding large-scale increases uncertainty and deforestation in the tropics risks for food production due is therefore beneficial at to direct physical changes both local and global scales. that alter temperature and rainfall, both near and far from where forests are cleared.
• Averages do not tell the • Adaptation is also critical whole story—equally as future crops will need to important are changes to tolerate changing, and wider local climate variability, ranges of, temperature and including how rainfall and rainfall patterns. temperature extremes are distributed, posing challenges for farmers that rely on predictable climates.