At the end of COP 21 (the 21st meeting of the conference of the parties at the conference chairing the conference), on 12 December 2015, the final text of the Paris Agreement was adopted by all 195 participating UNFCCC member states and by the European Union to reduce emissions under the method of reducing greenhouse gas emissions. In the 12-language agreement, members promised to reduce their carbon emissions «as soon as possible» and do their best to keep global warming «well below 2 degrees Celsius.»  At the same time, another study published in 2018 indicates that even with a warming of 1.5oC in India, South and Southeast Asia, we can expect a sharp increase in river flows.  However, the same study indicates that with a warming of 2oC, different regions of South America, Central Africa, Western Europe and the Mississippi region in the United States would be stronger; increase the risk of flooding. President Obama was able to formally enshrine the United States in the agreement through executive measures because he did not impose new legal obligations on the country. The United States already has a number of instruments on the books, under laws already passed by Congress to reduce carbon pollution. The country officially joined the agreement in September 2016, after submitting its request for participation. The Paris Agreement was only able to enter into force after the formal accession of at least 55 nations representing at least 55% of global emissions. This happened on October 5, 2016 and the agreement came into force 30 days later, on November 4, 2016. By analysis by the Intergovernmental Panel on Climate Change (IPCC), a carbon «budget» based on total emissions of carbon dioxide into the atmosphere (relative to the annual emission rate) has been estimated to limit global warming to 1.5 degrees Celsius and 2.25 trillion tonnes from the 1870 period. This represents a significant increase from the initial estimates of the Paris climate agreement (out of a total of 2000 billion tonnes) to reach the global warming target of 1.5oC, a target that would be reached in 2020 for 2017 emission rates. [Clarification needed] In addition, annual CO2 emissions are estimated at 40 billion tonnes per year in 2017. The revised IPCC budget was based on the CMIP5 climate model.
Estimate models using different reference years also provide other slightly adjusted estimates of a carbon «budget.»  As shown in the graph above, other steps have been taken since 1992 in negotiations at events such as the COP (Conference of the Parties). Below are the main agreements on climate change: warmer temperatures, both on land and at sea, change global weather and change how and where precipitation falls. These changing patterns exacerbate dangerous and deadly droughts, heat waves, floods, forest fires and storms, including hurricanes. They also melt ice caps, glaciers and permafrost layers, which can lead to sea level rise and coastal erosion. Warmer temperatures also affect entire ecosystems, deterring migration patterns and life cycles. For example, an early spring can make trees and plants bloom before bees and other pollinators are born. While global warming may be akin to longer growing periods and increased food production in some areas, areas already facing water shortages are expected to become drier and create potential for drought, broken harvests or forest fires.