What is the Evidence?

Gracier in front of Mountains

The Earth had had a climate long before humans roamed the plains. The climate is influenced by a whole series of cycles of glacial advance and retreat, that has been turning for hundreds of millions of years. Cataloguing climate change from the past creates a database that provides evidence that recent climate change is different from anything this planet has previously known. Scientists have calculated that it is more than 95 per cent probable that the current warming of the planet over the last seventy years is the result of human activity, with the rate of change faster than anything ever recorded over the last millennia.

Modern technology

With satellites orbiting the Earth collecting information, scientists have been able to look at the climate on a global scale. Ice cores show how the Earth’s climate has responded to changes in greenhouse gas levels over the last 800,000 years. Add in information from tree rings, ocean sediments, coral reefs, and layers of sedimentary rocks, and there is now a broad base of paleoclimate evidence that the global warming recorded today is about ten times faster than average.

Global Temperature Rise

The planet's average surface temperature has increased by about 0.8C (1.4F) in the last 150 years. Carbon dioxide levels have risen by more than 30 per cent, and methane levels have risen more than 140 per cent. About 0.6C (1.0F) of global warming has taken place in the last four decades, and the concentration of CO2 in the atmosphere is now higher than at any time in 800,000 years.

Global temperature difference

Warming Oceans

Covering 70 per cent of the Earth’s surface, the ocean has a major role in soaking up the heat and distributing it more evenly across the globe, as well as absorbing the Earth’s carbon dioxide. Since 1969, scientists have recorded the heat absorbed by the oceans, which has seen the top 700 metres (approximately 2,300 feet) increase by 0.4 degrees Fahrenheit, which affects life the algae, coral and fish in the oceans.

Shrinking Ice Sheets

Between 1993 and 2016, Greenland lost an average of 286 billion tons of ice per year and Antarctica lost about 127 billion tons of ice per year over the same period. In 2016, the scientific community hypothesised that the shrinking ice sheets would raise the sea level three feet by 2100. However, in February 2019, new research revised the estimates downward to between about three to 16 inches in the “worst case” scenarios.

Glacial Retreat

Records of glacier length go back over 400 years and show that the shrinking of mountain glaciers worldwide is almost certainly linked to global warming. Although the study of human influence on observed changes in temperature, rainfall, and other climate parameters is still in its infancy, scientists believe the near-global retreat of these rivers of ice is almost certainly due to human-caused climate change. Low latitude glaciers will disappear in the coming centuries as the planet warms. Though how quickly and by how much remains unknown.

Decreased Snow Cover

Satellite observations have shown that the amount of spring snow cover on land in the Northern Hemisphere has decreased over the past 50 years and that the snow is melting earlier. The data was originally collected for meteorological purposes, not for climate analysis and shows considerable seasonal variation which masks any long-term trend. Summer snow cover has reduced, but not in winter. In fact, the winter snow cover in 2009/2010 was the highest since 1978 and the second highest on record.

Sea Level Rise

Satellite data shows an average increase in global sea levels of about three millimetres per year, but in the twentieth century, the global sea level rose about eight inches. In the last two decades, it has risen 15 inches and increasing each year. A large proportion of the change in sea level is due to the fact that when seawater warms up, the molecules become less densely packed, causing an increase in the ocean’s volume.

Declining Arctic Sea Ice

Both the extent and thickness of Arctic sea ice has declined rapidly over several decades, melting faster than it re-freezes in winter, which the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report blames on greenhouse gases. The region is at its warmest for at least 4,000 years, leading to the Arctic-wide melt season increasing by five days every decade over the last 40 years, with a later freeze-up in the autumn.

Extreme Events

The increased risk of floods, heatwaves and wildfires have been recorded in the last few decades and has already been proven to be due to human-caused climate change. Carbon Brief, a UK-based website covering climate science, has found that 68 per cent of all extreme weather events studied in the last 20 years were made more likely or more severe by human-caused climate change.

Ocean Acidification

Over the past 200 years, the pH level of the ocean surface has lowered by 0.1 units, which represents a 30 per cent increase in acidity, and will soon have the highest pH levels estimated in twenty million years. Some marine life has been unable to adapt to the higher levels of acidity, unable to form strong shells or being poisoned in their new environment. This alters the ocean’s food chain, is dangerous for biodiversity both for marine life as well as human lives who depend on the seas for food and employment.