Past, Present, and Future

The yellow projection (C3) tells us what would happen if CO₂ concentrations were held steady at year 2000 levels. In other words, what would happen if humanity had suddenly stopped emitting CO₂ in the year 2000. Even in this imaginary case, temperatures would still continue to increase due to the thermal inertia of the oceans.

Where is Global Warming going?

US$ / Yen intervention

Negatives of Global Warming

Agriculture ·                     Decreasing human water supplies, increased fire frequency, ecosystem change and expanded deserts (Solomon 2009) ·                     Decline in rice yields due to warmer nighttime minimum temperatures (Peng 2004, Tao 2008) ·                     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 ·                            Increased deaths to heatwaves - 5.74% increase to heatwaves 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 ·                     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 ·                            Rainforests releasing CO2 as regions become drier (Saleska 2009) ·                            Extinction of the European land leech (Kutschera 2007) ·                            Decrease in Adélie penguin numbers  (Ducklow 2006) ·                            Disruption to New Zealand aquatic species such as salmonids, stream invertebrates, fishes (Ryan 2007) ·                            Oxygen poor ocean zones are growing  (Stramma 2008, Shaffer 2009) ·                            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 diseased driven by warming waters (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 ·                     Substantial negative impacts to marine ecosystems (Orr 2005, Fabry 2008,Kroeker 2010) ·                     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 one-sixth of world's population dependent on ice and snow melt for water supply (Barnett 2005) ·                            Contribution to rising sea levels (Pfeffer 2008, Vermeer 2009)

Economical ·                     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)

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How do we know global warming is not a natural cycle?

Several reasons. First, we know that burning coal, oil, and gas releases heat-trapping carbon dioxide, or CO2. And we know, thanks to careful measurements that started in the late 1950s, that CO2 levels in the atmosphere have been steadily climbing as we burn more. Not only that — chemists can tell the difference between the CO2 released naturally by plants and animals and the CO2 from burning fossil fuels. About a quarter of the CO2 now in the atmosphere is the result of human activity.

The one obvious natural suspect — the Sun — can pretty much be ruled out. It is an obvious suspect because astronomers know that the Sun can vary in brightness. When it does, the amount of heat it sends to the Earth varies too. It would not take much brightening to cause the increases in temperature we have seen. But satellites have been monitoring the Sun since the 1970s — when the fastest warming has been taking place — and the brightening just is not there.

There is plenty of other evidence — the pattern of warming, for example, which is greatest in the Arctic, and the pace, which is faster (as best we can tell) than prehistoric warming episodes. The upper atmosphere has actually cooled, because so much heat has been trapped below.

The bottom line is that nobody has come up with a natural explanation for the current warming episode that fits the observations. At the same time, the un-natural explanation—that our industrial civilization is a big part of the cause—fits the evidence.

That’s how we know it is not natural. One last thing. If the Earth has survived earlier warming episodes, what is so bad about this one even if it is not natural? The problem is that our civilization — where cities are located, where we grow food, where we get fresh water—is all based on the climate we have experienced for the last 10,000 years. So are many of the world’s ecosystems. If the climate changes, many of those things will suddenly find themselves in the wrong place.

How do we know?

Two NASA satellites, known as ACE and STEREO, measure the brightness of the Sun from Earth orbit, where the dimming effects of our atmosphere are minimal. Another satellite, called Aqua, looks down with an instrument called AIRS at the atmosphere from above to measure how much carbon dioxide is in it. And, as we discussed in the answer to the first question, we are measuring the Earth’s radiation budget from space.

From Climate Central