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The UN will host the 21st Conference of Parties (COP) in Paris in December later this year, and the focus is going to be on global climate change. Most of the leading nations in the world have been asked to pledge to keep the rise in global temperature under two degrees Celsius. This two-degree target was decided back in 2009 at another UN conference in Copenhagen, but why did they choose it? It can be traced back to two papers published in the mid-70s by Professor of Economics William Nordhaus at Yale University where he said, "If there were global temperatures more than two or three degrees above the current average temperature, this would take the climate outside of the range of observations which have been made over the last several hundred thousand years". Ice core sampling in the mid-1980s confirmed that two degrees above pre-industrial levels hadn't been seen on the planet in at least the last 100,000 years. Another report published in the 90s reconfirmed the consensus that two degrees is, "an upper limit beyond which the risks of grave damage to ecosystems...are expected to increase rapidly".
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This two degrees may seem insignificant, but this alone could cause significant impact on a number of ecosystems. A study published in the journal Nature Climate Change found that global sea levels could rise between 5 and 50 feet (1.5 and 4 meters) by the year 2300 if the Earth warms at least 2 degrees. In addition to rising oceans, many rivers could run dry, according to a study published in the journal Philosophical Transactions of the Royal Society A. In analyzing water scarcity, researchers found that water supplies would dwindle due to more pressure from growing populations. If the temperatures climb even higher, some river beds will be drier while others might be wetter. Additionally, as temperatures get increase, we are also seeing more extreme weather. In another study, researchers found other effects of temperature increases include no sea ice in the arctic during the summer, coral reef deaths, melting of permafrost which will release more greenhouse gases into the atmosphere, and significant shrinking of the Amazon rainforest. The study also predicts that semi-arid and arid places, like sub-Saharan Africa will become even drier, which could lead to a collapse of agricultural systems in that region.
So it's safe to say that if the world warms up even slightly, as it looks like it very well may be, the Earth is going to look a lot different than it does today.
Significant sea-level rise in a two-degree warmer world (Science Daily)
"Even if global warming is limited to two degrees Celsius, global mean sea level could continue to rise, reaching between 1.5 and four meters above present-day levels by the year 2300, with the best estimate being at 2.7 meters, according to a new study."
Water availability in +2°C and +4°C worlds (The Royal Society)
"While the parties to the UNFCCC agreed in the December 2009 Copenhagen Accord that a 2°C global warming over pre-industrial levels should be avoided, current commitments on greenhouse gas emissions reductions from these same parties will lead to a 50?:?50 chance of warming greater than 3.5°C."