We know the planet is slowly getting warmer, but how warm can it get. One of the main concerns is the rise in the sea level. If warming continues and exceeds 2ºC, Antarctica’s melting ice sheets could raise seas 20 meters in the coming centuries. In the past, 3 million years ago during the Pliocene epoch up to one-third of Antarctica’s ice sheets melted, causing the sea level to rise as much as 25m above present levels. According to the Paris Agreement signed in 2015, the world should avoid a temperature increase of more than 2ºC. One third of Antarctica’s ice sheet, equivalent to up to 20 m sea level rise, sits below sea level and is vulnerable to collapse from ocean heating. It melted sometimes in the past.
The Paris Agreement target about not exceeding 2ºC is important. The Paris Agreement (French: Accord de Paris) is an agreement within the United Nations Framework Convention on Climate Change (UNFCCC). This deals with greenhouse gas emissions mitigation, adaptation and finance. It was signed in 2016. As of March 2019, 195 UNFCCC members have signed the agreement, and 186 have become party to it. The Paris Agreement's long-term temperature goal is to keep the increase in global average temperature to well below 2 °C above pre-industrial levels; and to pursue efforts to limit the increase to 1.5 °C, recognizing that this would substantially reduce the risks and impacts of climate change. This should be done by peaking emissions as soon as possible, in order to "achieve a balance between anthropogenic emissions by sources and removals by sinks of greenhouse gases" in the second half of the 21st century. It also aims to increase the ability of parties to adapt to the adverse impacts of climate change, and make "finance flows consistent with a pathway towards low greenhouse gas emissions and climate-resilient development."
Under the Paris Agreement, each country must determine, plan, and regularly report on the contribution that it undertakes to mitigate global warming. No mechanism forces a country to set a specific target by a specific date, but each target should go beyond previously set targets. In June 2017, the U.S. President announced his intention to withdraw the United States from the agreement. Under the agreement, the earliest effective date of withdrawal for the U.S. is November 2020.