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.”  Nature studies indicate that from 2017 on none of the major industrialized countries implemented the strategies they had planned and did not meet the emission reduction targets they had promised, and even if this were the case, the sum of all accession commitments (from 2016) would not keep the global temperature increase “well below 2oC”.   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. Since November 2020, 194 states and the European Union have signed the agreement.
187 countries and the EU, which account for about 79% of global greenhouse gas emissions, have ratified the agreement or have joined the agreement, including China and India, the countries with the first and third largest CO2 emissions among UNFCCC members.    As of November 2020[update], the United States, Iran and Turkey are the only countries with more than 1% not to be contracting parties. The United States, the world`s second-largest emitter, is the only country to withdraw from the agreement, a move by President Donald J. Trump that came into effect in November 2020. Some other countries have not officially approved the agreement: Angola, Eritrea, Iran, Iraq, Libya, South Sudan, Turkey and Yemen. Paris Agreement, 2015. The most important global agreement to date, the Paris Agreement, obliges all countries to make commitments to reduce emissions. Governments set targets known as national contributions, with a view to preventing the average global temperature from rising by 2 degrees Celsius above pre-industrial levels and to strive to keep it below 1.5 degrees Celsius.