Carbon dioxide, nitrous oxide and methane are gases that accumulate in the atmosphere and prevent heat from radiating from the Earth`s surface into space, creating the so-called greenhouse effect. According to the Intergovernmental Panel on Climate Change (IPCC), the leading international scientific body working on the issue, the concentration of these heat storage gases has increased dramatically since pre-industrial times to levels not seen in at least 800,000 years. Carbon dioxide (the main cause of climate change) has increased by 40%, nitrous oxide by 20% and methane by 150% since 1750 – mainly from the combustion of dirty fossil fuels. The IPCC says it is « extremely likely » that these emissions are mainly responsible for the rise in global temperatures since the 1950s. At the same time, deforestation and forest degradation have also contributed to their fair share of global carbon emissions. At the end of the day, it all comes down to risk management. The greater our efforts to reduce greenhouse gas emissions, the lower the risk of extreme climate impacts. The higher our emissions, the greater the climate change we will face, which also means more costly adaptation, more species extinction, more food and water insecurity, more loss of income, more conflict, etc.  Under U.S. law, a president may, under certain circumstances, authorize U.S. participation in an international agreement without submitting it to Congress. Important considerations include whether the new agreement implements an earlier agreement, such as the UNFCCC, ratified with the approval of the Council and Senate, and whether it is compatible with existing US law and can be implemented on the basis of that law.
Since the agreement does not include binding emissions targets or binding financial commitments beyond those contained in the UNFCCC, and can be implemented on the basis of existing laws, President Obama has decided to approve it through executive action. In 2004, geologist and historian of science Naomi Oreskes summarized a review of the scientific literature on climate change.  It analyzed 928 abstracts of peer-reviewed scientific journal articles between 1993 and 2003 and concluded that there is a scientific consensus on the reality of anthropogenic climate change. A question that often arises in popular discussion is whether there is a scientific consensus on climate change.  Several scientific organizations have explicitly used the term « consensus » in their statements: the Paris Agreement establishes a global framework to avoid dangerous climate change by limiting global warming to well below 2°C and striving to limit it to 1.5°C. It also aims to strengthen the capacity of countries to cope with the effects of climate change and to support them in their efforts. Professor John Shepherd of the National Centre for Oceanography at the University of Southampton says the deal contains welcome aspirations, but few people know how difficult it will be to achieve the goals. The problems of global warming, climate change and their various negative effects on human life and on the functioning of entire societies are one of the most dramatic challenges of modern times. The Paris Agreement is the world`s first comprehensive climate agreement.  The Paris Agreement provides a sustainable framework that will guide global efforts in the coming decades. The goal is to create a continuous cycle that keeps pressure on countries to increase their ambitions over time.
In order to promote growing ambitions, the agreement introduces two interdependent processes, each of which spans a five-year cycle. The first process consists of a « global stocktaking » to assess collective progress towards the long-term goals of the agreement. The parties will then present new NDCs « based on the results of the global stocktake ». The globe is warming due to increasing greenhouse gas emissions. Measurements show that greenhouse gas concentrations in the atmosphere are well above the level observed for thousands of years. Further global climate change is predicted, with impacts expected to become more costly over time. Reducing the future impacts of climate change requires a significant reduction in greenhouse gas emissions.  In February 2007, following the publication of the IPCC`s Fourth Assessment Report, the Royal Meteorological Society approved the report. Not only did they call the IPCC « the best climate scientists in the world, » but they also said that climate change « is the result of emissions since industrialization and that we have already set in motion the next 50 years of global warming – what we do from now on will determine how much worse it will get. »  Some scientific panels have recommended specific policies to governments, and science can play a role in providing information on an effective response to climate change. However, policy decisions may require value judgments and are therefore not included in the scientific opinion.   Vox explains why scientists are more confident than ever that climate change is causing disasters.
There is a lot of misinformation about the Paris Agreement, including the idea that it will hurt the U.S. economy. It was a series of unsubstantiated claims that Trump repeated in his 2017 rose garden speech, claiming the deal would cost the United States. The economy is worth $3 trillion by 2040 and $2.7 million in jobs by 2025, making us less competitive with China and India. But as fact-checkers noted, these statistics come from a debunked March 2017 study that exaggerated the future costs of emission reductions, underestimated advances in energy efficiency and clean energy technologies, and completely ignored the huge health and economic costs of climate change itself. However, scientists point out that the Paris Agreement needs to be tightened if it is to have a chance of curbing dangerous climate change. Previous commitments could raise global temperatures by up to 2.7°C, but the agreement sets out a roadmap to accelerate progress. This CFR backgrounder compares the actions countries are taking to combat climate change. Although the agreement was welcomed by many, including French President François Hollande and UN Secretary-General Ban Ki-moon, criticism also surfaced. For example, James Hansen, a former NASA scientist and climate change expert, expressed anger that most of the deal is made up of « promises » or goals, not firm commitments.  He called the Paris talks a fraud with « nothing to do, only to promise » and believes that only a general tax on CO2 emissions, which is not part of the Paris Agreement, would reduce CO2 emissions fast enough to avoid the worst effects of global warming.
 Human activities are most likely responsible for global warming. Most of the global warming over the past 50 years has likely been caused by increased concentrations of greenhouse gases in the atmosphere. Long-term documented climate change includes changes in Arctic temperatures and ice, widespread changes in precipitation, ocean salinity, wind patterns, and extreme weather such as droughts, heavy rains, heat waves, and tropical cyclone intensity. The above development can have dramatic consequences for the future of humanity.  Global climate change and global warming are real and observable. It is very likely that human activities that have increased the concentration of greenhouse gases in the atmosphere have been largely responsible for the warming observed since 1950. The warming associated with the increase in greenhouse gases resulting from human activities is called the increase in the greenhouse effect. The atmospheric concentration of carbon dioxide has increased by more than 30% since the beginning of the industrial era and is now higher than ever in the last 650,000 years.
This increase is a direct result of fossil fuel combustion, large-scale deforestation and other human activities.  In agreements adopted in Copenhagen in 2009 and Cancún in 2010, governments set a goal of keeping global temperature rise below 2 degrees Celsius above pre-industrial levels. The Paris Agreement reaffirms the 2 degree target and urges efforts to limit the increase to 1.5 degrees Celsius. The agreement also sets two other long-term reduction targets: first, a peak in emissions as soon as possible (recognising that this will take longer for developing countries); Then a goal of net neutrality in greenhouse gases (« a balance between anthropogenic emissions from sources and removals from sinks ») in the second half of the century. To counter climate change and its negative effects, 197 countries adopted the Paris Agreement at COP21 in Paris on 12 December 2015. The agreement, which entered into force less than a year later, aims to significantly reduce global greenhouse gas emissions and limit the rise in global temperature to 2 degrees Celsius this century, while looking for ways to further limit the increase to 1.5 degrees. .