A fairly small increase in average global temperature can lead to changes in rainfall patterns, rises in sea levels, melting of the ice caps and widespread flooding. Evidence continues to accumulate that increases in atmospheric carbon dioxide and other "greenhouse gases" (carbon dioxide, chlorofluorocarbons, methane, nitrogen oxides, ozone, halocarbons, and others) are substantially raising the global temperature.
 A global surface warming of between 0.3 and 0.6°C (degrees Celsius) has taken place over the past century. Estimated global temperature for 1992 and 1993 remain about 0.13 and 0.19°C warmer than 1951-80 norms. 1997 was the warmest year on record. The warmest years of the century have all occurred since 1979.
The UN intergovernmental panel on climate change, underpinned by thousands of scientists worldwide, has concluded that there is a "discernible human influence" on the global climate. Corresponding to a doubling of pre-industrial levels of carbon dioxide (CO2) in the atmosphere by 2050, the IPPC has forecast that global average temperatures will rise by between 1.4 to 5.8 degrees centigrade by 2100. It is worth remembering that the last ice age, when much of the Northern Hemisphere was buried under an ice-pack thousands of feet thick, was triggered by a fall in temperature of only some five degrees centigrade.
When the UN’s Paris Agreement was adopted in December 2015, it defined a specific goal: to keep global warming to well below 2°C and as close as possible to 1.5°C above pre-industrial levels (defined as the climate conditions experienced during the 1850–1900 period). While admirable in intent, the agreement did not impose legally binding limits on signatory nations and contained no enforcement mechanisms. Instead, each country committed to publicly disclosed Nationally Determined Contributions (NDCs) to reduce emissions. In essence, it is up to each nation to act in the public interest.
In 2017, we reached 1°C of warming above global pre-industrial conditions. According to the UN Environment Programme’s “Emissions Gap Report”, released in November 2018, current unconditional NDCs will see global average temperature rise by 2.9 to 3.4°C above pre-industrial levels by the end of this century.
To restrict warming to 2°C above pre-industrial levels, the world needs to triple its current emission reduction pledges. If that’s not bad enough, to restrict global warming to 1.5°C, global ambition needs to increase fivefold.
In 1994, it was reported that trend studies in regions as diverse as North America, India, the Middle East and New Zealand have consistently showed strong but seasonally and geographically variable warming (with greatest warming generally in the spring season). While studies comparing these observed trends against a combination of climate forcings, including solar, volcanic, El NiÃ±o and greenhouse gases, still fail to prove conclusively that the trends are caused by the enhanced greenhouse effect, they do provide strong evidence that it is a significant factor.
Scientists at the US National Oceanic and Atmospheric Administration and the British Meteorological Office have produced evidence that 1997 was the warmest recorded year since record keeping began. Bolstered by exceptionally warm temperatures in December, the global average temperature for 1997 was at 62.45 degrees Fahrenheit (16.92 degrees centigrade) - three-quarters of a degree higher the "normal" average for the past 30 years, and 0.15 degrees warmer than the previous record high set in 1990.
While there are local differences, the average temperature in Europe has increased by 0.8 degrees centigrade since 1990. Greater precipitation has been documented in the northern half of Europe, with increases ranging from 10% to 50%. In an area stretching from the Mediterranean through central Europe into the European part of the Russian Federation and Ukraine, by contrast, precipitation has decreased by as much as 20%.
On 12 January 1999 NASA scientists announced that 1998 was the warmest recorded year in history. "There should no longer be an issue about whether global warming is occurring, but what is the rate of warming, what is its practical significance and what should be done about it," said Dr. James Hansen, a scientist with the NASA Goddard Institute for Space Studies. The NASA report concluded that the average worldwide temperature in 1998 was 58.496 degrees, topping the record of 58.154 degrees set in 1995. NASA researchers collecting data from thousands of meteorological stations around the world have concluded that although some natural phenomena may have contributed to the warming, the planet is exiting the range of normal climatic variability.
An interagency report, compiled by the US Environmental Protection Agency, notes that the warming of the US is expected to be greater in the 21st century than in the 20th, and will affect nearly every region of the country. Sea levels would rise quickly, threatening low-lying and storm-raked areas like Long Island and coastal wetlands. Storm surges will pose a greater threat to coastal communities. There will be more stifling heat waves and the disruption of snow-fed water supplies. In the mountains of New York and New England, winter would disappear and the forests that make the fall spectacular would wither. Some treasured ecosystems, such as the Rocky Mountain meadows and certain coral reefs and barrier islands, are likely to disappear entirely. Some areas are already experiencing a shorter duration of lake ice and there has been a northward shift in the distributions of some species of butterflies.
In Fairbanks Alaska the number of days 40-below in the late 1990s is half what it was in the 1950s. The permafrost is warming by an estimated two to four degrees centigrade. Sea ice is shrinking.EPn the Bering sea it has reduced by about 5% over the last 40 years.
The southern half of Greenland's ice sheet is melting according to scientists. Between 1993 and 1998 the ice cap on Greenland has shrunk substantially, by an average of two cubic miles of ice each year. Whilst acknowledging that five years is not enough to establish a trend, scientists are surprised by the magnitude of the shrinkage. Even a partial melting of the ice cap could have significant effects on the worlds climate and regulatory systems.
Almost two million homes in England and Wales are at risk from floods, and Britain will experience a 65% increase in river flooding if defences do not account for climate change.