Efforts to scientifically ascertain and attribute mechanisms responsible for recent global warming and related climate changes on Earth have found that the main driver is elevated levels of greenhouse gases produced by human activities, with natural forces adding variability. The likely range of human-induced surface-level air warming by 2010–2019 compared to levels in 1850–1900 is 0.8 °C to 1.3 °C, with a best estimate of 1.07 °C. This is close to the observed overall warming during that time of 0.9 °C to 1.2 °C, while temperature changes during that time were likely only ±0.1 °C due to natural forcings and ±0.2 °C due to variability in the climate.
Benjamin David Santer is a climate researcher at Lawrence Livermore National Laboratory and former researcher at the University of East Anglia's Climatic Research Unit. He also worked at the Max Planck Institute for Meteorology from 1987 to 1992. He specializes mainly in statistical analysis of climate data sets, and detection/attribution of climate change forcings.
Climate is the long-term weather pattern in a region, typically averaged over 30 years. More rigorously, it is the mean and variability of meteorological variables over a time spanning from months to millions of years. Some of the meteorological variables that are commonly measured are temperature, humidity, atmospheric pressure, wind, and precipitation. In a broader sense, climate is the state of the components of the climate system, including the atmosphere, hydrosphere, cryosphere, lithosphere and biosphere and the interactions between them. The climate of a location is affected by its latitude, longitude, terrain, altitude, land use and nearby water bodies and their currents.
The global warming controversy concerns the public debate over whether global warming is occurring, how much has occurred in modern times, what has caused it, what its effects will be, whether any action can or should be taken to curb it, and if so what that action should be. In the scientific literature, there is a very strong consensus that global surface temperatures have increased in recent decades and that the trend is caused by human-induced emissions of greenhouse gases. No scientific body of national or international standing disagrees with this view, though a few organizations with members in extractive industries hold non-committal positions, and some have tried to persuade the public that climate change is not happening, or if the climate is changing it is not because of human influence, attempting to sow doubt in the scientific consensus.
The instrumental temperature record is a record of temperatures within Earth's climate based on direct, instrument-based measurements of air temperature and ocean temperature. Instrumental temperature records are distinguished from indirect reconstructions using climate proxy data such as from tree rings and ocean sediments. Instrument-based data are collected from thousands of meteorological stations, buoys and ships around the globe. Whilst many heavily-populated areas have a high density of measurements, observations are more widely spread in sparsely populated areas such as polar regions and deserts, as well as over many parts of Africa and South America. Measurements were historically made using mercury or alcohol thermometers which were read manually, but are increasingly made using electronic sensors which transmit data automatically. Records of global average surface temperature are usually presented as anomalies rather than as absolute temperatures. A temperature anomaly is measured against a reference value. For example, a commonly used baseline period is the time period 1951-1980.
The temperature record of the last 2,000 years is reconstructed using data from climate proxy records in conjunction with the modern instrumental temperature record which only covers the last 170 years at a global scale. Large-scale reconstructions covering part or all of the 1st millennium and 2nd millennium have shown that recent temperatures are exceptional: the Intergovernmental Panel on Climate Change Fourth Assessment Report of 2007 concluded that "Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1,300 years." The curve shown in graphs of these reconstructions is widely known as the hockey stick graph because of the sharp increase in temperatures during the last century. As of 2010 this broad pattern was supported by more than two dozen reconstructions, using various statistical methods and combinations of proxy records, with variations in how flat the pre-20th-century "shaft" appears. Sparseness of proxy records results in considerable uncertainty for earlier periods.
There is a strong scientific consensus that the Earth is warming and that this warming is mainly caused by human activities. This consensus is supported by various studies of scientists' opinions and by position statements of scientific organizations, many of which explicitly agree with the Intergovernmental Panel on Climate Change (IPCC) synthesis reports.
Thomas R. Karl is the former director of the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information (NCEI). He joined the National Climate Centre in 1980, and when that became the National Climatic Data Center, he continued as a researcher, becoming a Lab Chief, Senior Scientist and ultimately Director of the Center. When it merged with other centers to become NCEI in 2015, he became its first director. He retired on 4 August 2016.
Sir John Theodore Houghton was a Welsh atmospheric physicist who was the co-chair of the Intergovernmental Panel on Climate Change's (IPCC) scientific assessment working group which shared the Nobel Peace Prize in 2007 with Al Gore. He was the lead editor of first three IPCC reports. He was professor in atmospheric physics at the University of Oxford, former Director General at the Met Office and founder of the Hadley Centre.
The IPCC Third Assessment Report (TAR), Climate Change 2001, is an assessment of available scientific and socio-economic information on climate change by the IPCC. Statements of the IPCC or information from the TAR were often used as a reference showing a scientific consensus on the subject of global warming. The Third Assessment Report (TAR) was completed in 2001 and consists of four reports, three of them from its Working Groups: Working Group I: The Scientific Basis; Working Group II: Impacts, Adaptation and Vulnerability; Working Group III: Mitigation; Synthesis Report. A number of the TAR's conclusions are given quantitative estimates of how probable it is that they are correct, e.g., greater than 66% probability of being correct. These are "Bayesian" probabilities, which are based on an expert assessment of all the available evidence.
Jonathan Michael Gregory is a climate modeller working on mechanisms of global and large-scale change in climate and sea level on multidecadal and longer timescales at the Met Office and the University of Reading.
Climate change affects the physical environment, ecosystems and human societies. Changes in the climate system include an overall warming trend, more extreme weather and rising sea levels. These in turn impact nature and wildlife, as well as human settlements and societies. The effects of human-caused climate change are broad and far-reaching. This is especially so if there is no significant climate action. Experts sometimes describe the projected and observed negative impacts of climate change as the climate crisis.
Climate change conspiracy theories assert that the scientific consensus on global warming is based on conspiracies to produce manipulated data or suppress dissent. It is one of a number of tactics used in climate change denial to attempt to manufacture political and public controversy disputing this consensus. Conspiracy theorists typically allege that, through worldwide acts of professional and criminal misconduct, the science behind global warming and climate change has been invented or distorted for ideological or financial reasons.
Piers Forster is a Professor of Physical Climate Change and Director of the Priestley International Centre for Climate at the University of Leeds. A physicist by training, his research focuses on quantifying the different human causes of climate change and the way the Earth responds. He is best known for his work on radiative forcing, climate sensitivity, contrails and Climate engineering. He has contributed heavily to the writing of Intergovernmental Panel on Climate Change (IPCC) reports, including acting as a Lead Author for the Fourth and Fifth Assessment Reports, and a Co-ordinating Lead Author for the Sixth Report. He also acted as a Lead Author of the IPCC 2018 Special Report on Global Warming of 1.5 °C.
Richard Arthur Betts is Head of the Climate Impacts strategic area at the Met Office Hadley Centre in Exeter, United Kingdom. He is also chair in Climate Impacts at the University of Exeter and the Principal Investigator of the EU FP7 project HELIX. He was a lead author for Working Group I and a contributing author for Working Group II of the IPCC Fourth Assessment Report. He was a lead author for Working Group II of the IPCC Fifth Assessment Report. He is an editor for the International Journal of Global Warming, the Journal of Environmental Investing, and for Earth System Dynamics. He was appointed MBE in the 2019 Birthday Honours.
The Tempestry Project is a collaborative fiber arts project that presents global warming data in visual form through knitted or crocheted artwork. The project is part of a larger "data art" movement and the developing field of climate change art, which seeks to exploit the human tendency to value personal experience over data by creating accessible experiential representations of the data.
Climate change art is art inspired by climate change and global warming, generally intended to overcome humans' hardwired tendency to value personal experience over data and to disengage from data-based representations by making the data "vivid and accessible". One of the goal of climate change art is to "raise awareness of the crisis", as well as engage viewers politically and environmentally.
Warming stripes are data visualization graphics that use a series of coloured stripes chronologically ordered to visually portray long-term temperature trends. Warming stripes reflect a "minimalist" style, conceived to use colour alone to avoid technical distractions to intuitively convey global warming trends to non-scientists.
A climate spiral is an animated data visualization graphic designed as a "simple and effective demonstration of the progression of global warming", especially for general audiences.
Antje Weisheimer is a German climate scientist researching at the University of Oxford, UK, and the European Centre for Medium-Range Weather Forecasts, Reading, UK.
