Does global warming have an upside?
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Science says: Negative impacts of global warming on agriculture, health, and environment far outweigh any positives.

Agriculture

While CO2 is essential for plant growth, all agriculture depends also on steady water supplies, and climate change is likely to disrupt those supplies through floods and droughts. It has been suggested that higher latitudes—Siberia, for example—may become productive due to global warming, but the soil in Arctic and bordering territories is very poor, and the amount of sunlight reaching the ground in summer will not change because it is governed by the tilt of the earth. Agriculture can also be disrupted by wildfires and changes in seasonal periodicity, which is already taking place, and changes to grasslands and water supplies could impact grazing and welfare of domestic livestock. Increased warming may also have a greater effect on countries whose climate is already near or at a temperature limit over which yields reduce or crops fail—in the tropics or sub-Sahara, for example.

Health

Warmer winters would mean fewer deaths, particularly among vulnerable groups like the aged. However, the same groups are also vulnerable to additional heat, and deaths attributable to heat waves are expected to be approximately five times as great as winter deaths prevented. It is widely believed that warmer climes will encourage migration of disease-bearing insects like mosquitoes and malaria is already appearing in places it hasn't been seen before.

Polar Melting

While the opening of a year-round ice free Arctic passage between the Atlantic and Pacific oceans would confer some commercial benefits, these are considerably outweighed by the negatives. Detrimental effects include loss of polar bear habitat and increased mobile ice hazards to shipping. The loss of ice albedo (the reflection of heat), causing the ocean to absorb more heat, is also a positive feedback; the warming waters increase glacier and Greenland ice cap melt, as well as raising the temperature of Arctic tundra, which then releases methane, a very potent greenhouse gas (methane is also released from the sea-bed, where it is trapped in ice-crystals called clathrates). Melting of the Antarctic ice shelves is predicted to add further to sea-level rise with no benefits accruing.

Ocean Acidification

A cause for considerable concern, there appear to be no benefits to the change in pH of the oceans. This process is caused by additional CO2 being absorbed in the water, and may have severe destabilizing effects on the entire oceanic food-chain.

Melting Glaciers

The effects of glaciers melting are largely detrimental, the principle impact being that many millions of people (one-sixth of the world's population) depend on fresh water supplied each year by natural spring melt and regrowth cycles and those water supplies—drinking water, agriculture—may fail.

Sea Level Rise

Many parts of the world are low-lying and will be severely affected by modest sea rises. Rice paddies are being inundated with salt water, which destroys the crops. Seawater is contaminating rivers as it mixes with fresh water further upstream, and aquifers are becoming polluted. Given that the IPCC did not include melt-water from the Greenland and Antarctic ice-caps due to uncertainties at that time, estimates of sea-level rise are feared to considerably underestimate the scale of the problem. There are no proposed benefits to sea-level rise.

Environmental

Positive effects of climate change may include greener rain forests and enhanced plant growth in the Amazon, increased vegetation in northern latitudes and possible increases in plankton biomass in some parts of the ocean. Negative responses may include further growth of oxygen poor ocean zones, contamination or exhaustion of fresh water, increased incidence of natural fires, extensive vegetation die-off due to droughts, increased risk of coral extinction, decline in global photo-plankton, changes in migration patterns of birds and animals, changes in seasonal periodicity, disruption to food chains and species loss.

Economic

The economic impacts of climate change may be catastrophic, while there have been very few benefits projected at all. The Stern report made clear the overall pattern of economic distress, and while the specific numbers may be contested, the costs of climate change were far in excess of the costs of preventing it. Certain scenarios projected in the IPCC AR4 report would witness massive migration as low-lying countries were flooded. Disruptions to global trade, transport, energy supplies and labour markets, banking and finance, investment and insurance, would all wreak havoc on the stability of both developed and developing nations. Markets would endure increased volatility and institutional investors such as pension funds and insurance companies would experience considerable difficulty.

Developing countries, some of which are already embroiled in military conflict, may be drawn into larger and more protracted disputes over water, energy supplies or food, all of which may disrupt economic growth at a time when developing countries are beset by more egregious manifestations of climate change. It is widely accepted that the detrimental effects of climate change will be visited largely on the countries least equipped to adapt, socially or economically.

Science says: Negative impacts of global warming on agriculture, health, and environment far outweigh any positives.

The following is a list of positive and negative impacts of climate change that can be found in peer-reviewed literature.

Positive Impacts Negative Impacts

Agriculture

Improved agriculture in some high latitude regions (Mendelsohn 2006) Decreasing human water supplies, increased fire frequency, ecosystem change and expanded deserts (Solomon 2009)
Increased growing season in Greenland (Nyegaard 2007) Decline in rice yields due to warmer nighttime minimum temperatures (Peng 2004, Tao 2008)
Increased productivity of sour orange trees (Kimball 2007) Increase of Western United States wildfire activity, associated with higher temperatures and earlier spring snowmelt (Westerling 2006)
Encroachment of shrubs into grasslands, rendering rangeland unsuitable for domestic livestock grazing (Morgan 2007)
Decreased water supply in the Colorado River Basin (McCabe 2007)
Decreasing water supply to the Murray-Darling Basin (Cai 2008)

Health

Winter deaths will decline as temperatures warm (HPA 2007) Increased deaths to heat waves - 5.74% increase to heat waves compared to 1.59% to cold snaps (Medina-Ramon 2007)
Increased heat stress in humans and other mammals (Sherwood 2010)
Spread in mosquite-borne diseases such as Malaria and Dengue Fever (Epstein 1998)
Increase in occurrence of allergic symptoms due to rise in allergenic pollen (Rogers 2006)

Arctic Melt

An ice-free Northwest Passage, providing a shipping shortcut between the Pacific and Atlantic Oceans (Kerr 2002, Stroeve 2008) Loss of 2/3 of the world's polar bear population within 50 years (Amstrup 2007)
Less compacted ice, hazardous floes and more mobile icebergs posing increased risk to shipping (IICWG 2009)
Drying of arctic ponds with subsequent damage to ecosystem (Smol 2007)
Warming causes methane to escape from Arctic regions, contributing additional greenhouse warming. The following have been observed:
Melting of Arctic lakes leading methane bubbling (Walter 2007)
Leakage of methane from the East Siberian Shelf seabed sediments (Shakhova 2008)
Escape of methane gas from the seabed along the West Spitsbergen continental margin (Westbrook 2009)

Environment

Increased vegetation activity in high northern latitudes (Zhou 2001) Rainforests releasing CO2 as regions become drier (Saleska 2009)
Increase in chinstrap and gentoo penguins (Ducklow 2006) Extinction of the European land leech (Kutschera 2007)
Increased plankton biomass in the North Pacific Subtropical Gyre (arguably ENSO/PDO might be dominant influence) (Corno 2006) Decrease in Adelie penguin numbers  (Ducklow 2006)
Recent increase in forest growth (McMahon 2010) Disruption to New Zealand aquatic species such as salmonids, stream invertebrates, fishes (Ryan 2007)
Bigger marmots (Ozgul 2010) Oxygen poor ocean zones are growing  (Stramma 2008, Shaffer 2009)
Increased Arctic tundra plant reproduction (Klady 2010) Increased mortality rates of healthy trees in Western U.S. forest (Pennisi 2009)
More severe and extensive vegetation die-off due to warmer droughts (Breshears 2009)
Increased pine tree mortality due to outbreaks of pine beetles (Kurz 2008, Bentz 2010)
Increased risk of coral extinction from bleaching and disease driven by warming waters (Veron 2009, Carpenter 2008)
Decline in lizard populations (Sinervo 2010)
Decline in global phytoplankton (Boyce 2010)
Decline in global net primary production - the amount of carbon absorbed by plants (Zhao 2010)

Ocean Acidification

Note: this is not caused by warming temperatures but by the oceans absorbing more carbon dioxide (Dore 2009). Substantial negative impacts to marine ecosystems (Orr 2005, Fabry 2008, Kroeker 2010)
Oceans uptake of carbon dioxide, moderates future global warming (Orr 2005) Inhibiting plankton development, disruption of carbon cycle (Turley 2005)
Increased mortalities of sea urchins (Miles 2007)
Threat to fish populations (Munday 2010)

Glacier Melt

Severe consequences for at least 60 million people dependent on ice melt for water supply (Barnett 2005, Immerzeel 2010)
Contribution to rising sea levels (Pfeffer 2008, Vermeer 2009)

Economical

Increased cod fishing leading to improved Greenland economy (Nyegaard 2007) Economic damage to poorer, low latitude countries (Mendelsohn 2006)
Billions of dollars of damage to public infrastructure (Larsen 2007)
Reduced water supply in New Mexico (Hurd 2008)
Increased risk of conflict (Zhang 2007) including increased risk of civil war in Africa (Burke 2009)
Drop in primary productivity due to unprecedented warming at Lake Tanganyika (Tierney 2010)

Sea Level Rise

Hundreds of millions displaced within this century (Dasgupta 2009)
Coastal erosion in Nigeria (Okude 2006)

The myth:

"Two thousand years of published human histories say that warm periods were good for people. It was the harsh, unstable Dark Ages and Little Ice Age that brought bigger storms, untimely frost, widespread famine and plagues of disease."

Dennis Avery

About Skeptical Science

Skeptical Science was founded by physicist John Cook in 2007 to explore what science has to say about global warming. In 2011, Skeptical Science won the Australian Museum Eureka Prize for the Advancement of Climate Change Knowledge. It is not affiliated with any organization, and is funded by contributions from readers.

John Cook is the Climate Change Communication Fellow for the Global Change Institute at the University of Queensland. He created and runs skepticalscience.com. His efforts have concentrated on making climate science accessible to the general public, releasing smartphone apps for the iPhone and Android phones. He has produced climate communication resources adopted by organizations such as NOAA and the U.S. Navy, and co-authored the book Climate Change Denial: Heads in the Sand with environmental scientist Haydn Washington.