How do we know climate change is real? – Part 1

In the last 800,000 years, the Earth’s climate has changed eight times in ice ages and warmer periods. The last ice age was recorded and proven 11,700 years ago. So, how do we know current warming is not a periodic climate change?

1.  History

The current warming trend is different because it is clearly the result of human activities since the mid-1800s, and is proceeding at a rate not seen over many recent millennia. The data from measuring the temperature at weather stations and tracking surface with satellites all indicate the story: “Earth is getting warmer”. Human activities are strongly believed to be the main production of atmospheric gases which have trapped more Sun’s energy in the Earth system. This extra energy has warmed the atmosphere, ocean, and land, and widespread and rapid changes in the atmosphere, ocean, cryosphere, and biosphere have occurred.

This graph, based on the comparison of atmospheric samples contained in ice cores and more recent direct measurements, provides evidence that atmospheric CO2 has increased since the Industrial Revolution. (Credit: Luthi, D., et al.. 2008; Etheridge, D.M., et al. 2010; Vostok ice core data/J.R. Petit et al.; NOAA Mauna Loa CO2 record.) 

This warming is unprecedented in recent geologic history. A famous illustration, first published in 1998 and often called the hockey-stick graph, shows how temperatures remained fairly flat for centuries (the shaft of the stick) before turning sharply upward (the blade). It’s based on data from tree rings, ice cores and other natural indicators. Ancient evidence can also be found in ocean sediments, coral reefs, and layers of sedimentary rocks. This ancient, or paleoclimate, evidence reveals that current warming is occurring roughly 10 times faster than the average rate of warming after an ice age. Carbon dioxide from human activities is increasing about 250 times faster than it did from natural sources after the last Ice Age.

2.  Evidence

• Global Temperature is rising

The Earth’s average surface temperature has risen roughly 0.8° Celsius (1.4° Fahrenheit) since the early 20th century, a change driven largely by increased carbon dioxide emissions into the atmosphere and other human activities. The greenhouse effect is essential to life on Earth, but human-made emissions in the atmosphere are trapping and slowing heat loss to space. According to NASA, 2016 and 2020 are tied for the warmest year since 1880, continuing a long-term trend of rising global temperatures. On top of that, the nine most recent years have been the hottest.

• The Ocean is getting warmer

More than 90 percent of the warming that has happened on Earth over the past 50 years has occurred in the ocean. The ocean has absorbed much of this increased heat, with the top 100 meters (about 328 feet) of the ocean showing warming of more than 0.6 degrees Fahrenheit (0.33 degrees Celsius) since 1969.

• The Ice Sheets are shrinking

The Greenland and Antarctic ice sheets have decreased in mass. Data from NASA’s Gravity Recovery and Climate Experiment show Greenland lost an average of 279 billion tons of ice per year between 1993 and 2019, while Antarctica lost about 148 billion tons of ice per year.

• Glaciers are retreating

Glaciers are retreating almost everywhere around the world — including in the Alps, Himalayas, Andes, Rockies, Alaska, and Africa. Widespread loss of glaciers would likely alter climate patterns in complex ways. Glaciers have white surfaces that reflect the Sun’s rays. This helps keep our current climate mild. When glaciers melt, darker surfaces are exposed, which absorb heat. This raises temperatures even more.

• Snow cover is decreasing

Satellite observations reveal that the amount of spring snow cover in the Northern Hemisphere has decreased over the past five decades and the snow is melting earlier. In the high latitudes of the Northern Hemisphere, the rate of spring snow decline has been as dramatic as the rate of Arctic sea ice loss.

• Sea level is rising

Global sea level rose has risen about 8-9 inches (20-24 centimeters) since 1880. The rate in the last two decades, however, is nearly double that of the last century and accelerating slightly every year. The rising water level is mostly due to a combination of meltwater from glaciers and ice sheets and the thermal expansion of seawater as it warms.

• Extreme Events are increasing in frequency

The frequency of extreme weather events, including floods, storms, droughts, extreme temperatures, and wildfires, has intensified globally over recent decades due to climate. The U.S. has also witnessed increasing numbers of intense rainfall events. High-tide flooding is now 300% to more than 900% more frequent than it was 50 years ago. Climate-related disasters jumped 83 percent — from the 1980-1999 period to the past 20 years. Major floods have more than doubled, the number of severe storms has risen 40 percent, and there have been major increases in droughts, wildfires, and heatwaves.

• Ocean Acidification is Increasing

Since the beginning of the Industrial Revolution, the acidity of surface ocean waters has increased by about 30%, a pace faster than any known in Earth’s geologic past. This increase is due to humans emitting more carbon dioxide into the atmosphere and hence more being absorbed into the ocean. The ocean has absorbed between 20% and 30% of total anthropogenic carbon dioxide emissions in recent decades (7.2 to 10.8 billion metric tons per year).

In the next part, we will learn more about the accuracy of evidence and the reasons many people don’t believe in climate change.

Author: Trinh Thi Phuong Ly

References

1. Dahlman, R. L. A. N. D. L. A. (n.d.). Climate change: Ocean heat content. NOAA Climate.gov. Retrieved February 9, 2023, from https://www.climate.gov/news-features/understanding-climate/climate-change-ocean-heat-content
2. Environmental Protection Agency. (n.d.). Understanding the Science of Ocean and Coastal Acidification. EPA. Retrieved February 9, 2023, from https://www.epa.gov/ocean-acidification/understanding-science-ocean-and-coastal-acidification
3. How do we know climate change is happening? Imperial College London. (n.d.). Retrieved February 9, 2023, from https://www.imperial.ac.uk/grantham/publications/climate-change-faqs/how-do-we-know-climate-change-is-happening/
4. Lindsey, R. (n.d.). Climate change: Global sea level. NOAA Climate.gov. Retrieved February 9, 2023, from https://www.climate.gov/news-features/understanding-climate/climate-change-global-sea-level
5. Lindsey, R. (n.d.). Climate change: Spring snow cover in the Northern Hemisphere. NOAA Climate.gov. Retrieved February 9, 2023, from https://www.climate.gov/news-features/understanding-climate/climate-change-spring-snow-cover-northern-hemisphere
6. NASA. (2023, February 6). Climate change evidence: How do we know? NASA. Retrieved February 9, 2023, from https://climate.nasa.gov/evidence/#otp_history
7. NASA. (n.d.). Global ice viewer – climate change: Vital signs of the planet. NASA. Retrieved February 9, 2023, from https://climate.nasa.gov/interactives/global-ice-viewer#/1/about/1315