Published on: 12/21/2020 3:46:00 AM

The Earth's climate has changed throughout history. Just in the last 650,000 years there have been seven cycles of glacial advance and retreat, with the abrupt end of the last ice age about 7,000 years ago marking the beginning of the modern climate era - and of human civilization. Most of these climate changes are attributed to very small variations in earth's orbit that change the amount of solar energy our planet receives.

The current warming trend is of particular significances because most of it is extremely likely (>95% probability) to the result of human activity since the mid-20th century and preceding at a rate that is unprecedented over decades to millennia. Earth-orbiting satellites and other technological advances have enabled scientists to see the big picture, collecting many different types of information about our planet and its climate on a global scale. This body of data, collected over many years, reveals the signals of a changing climate.

The heat - trapping nature of carbon dioxide and other gases was demonstrated in the mid-19th century. Their ability to affect the transfer of infrared energy through the atmosphere is the scientific basis of many instruments flown by NASA. There is no question that increased levels of greenhouse gases must cause the earth to warm in response.

Ice cores drawn from Greenland, Antarctica, and tropical mountain glaciers show that the earth's climate responds to change in greenhouse gas levels Ancient evidence can also be found in tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidences reveals that current warming is occurring roughly ten times faster than the average rate of ice-age recovery warming.

Evidence for rapid climate change is compelling

 Global temperature rise: The Planet's average surface temperature has risen about 2.0° F (1.1° C) Since the Late 19th century, change driven largely by increased carbon dioxide and other human made emissions into the atmosphere. Most of the warming occurred in the past 35 years, with 16 of the 17 warmest years on record occurring since 2001. Not Only was 2016 the warmest year on record, but eight of the 12 months that make up the year.

Warming Oceans: The Oceans have absorbed much of this increased heat, with the top 700 mtr. (about 2,300 ft) of ocean showing warming of 0.302° F since 1969.

Shrinking ice sheets: The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA'S Gravity Recovery and climate Experiment show Greenland lost about 152 cubic kilometres of ice b/w 2002 and 2005.

Glacial retreat: Glaciers are retreating almost every-where around the world including in the Alps, Himalayas, Andes, Rockies, Alaska and Africa.

Decreased snow cover: Satellite observations reveal that the amount of spring snow cover in the North hemisphere has decreased over the past five decades and that the snow is melting earlier

Sea level rise: Global sea level rose about 8 inches in the last century. The rate in the last two decades, however, is nearly double that of the last century.

Declining Arctic Sea ice: Both the extent and thickness of Arctic sea ice has declined rapidly over the last several decades.

Extreme Events: The no. of record high temperature events in the world has been increasing, while the no. of record low temp. events has been decreasing since 1950.

Ocean acidification: Since the beginning of the Industrial Revolution, the acidity of surface ocean water has increased by about 30%. This increase is the result of humans emitting more CO2 into the atmosphere and hence more being absorbed into the oceans. The amount of CO2 absorbed by the upper layer of the oceans is increasing by about 2 billion tons per year.