The international community must take urgent action to curb greenhouse gas emissions in order to keep the temperature rise to well below 1.5°C above pre-industrial levels. How are greenhouse gases associated with human economic activities which are affecting climate change, and how are they predicted and monitored?

In a paper published in the journal Geophysical Science Research on March 25, 2021, NASA has confirmed with direct evidence that human activities are blocking the release of energy from sunlight back into space and changing the Earth's energy budget.

The earth is constantly trying to balance the inflow and outflow of energy from the sun. The energy from sunlight is reflected from the surface of the earth and the atmosphere and released into outer space, but the rest is absorbed and warms the earth in the same way that asphalt heats up on a hot sunny day. Eventually, this heat is also released into outer space, but it is blocked and re-absorbed by clouds and greenhouse gases in the atmosphere, warming the earth. It is said that global warming occurs when greenhouse gases are accumulated by artificial economic activities and the energy that should be released into outer space is absorbed by the earth. This process of human activity affecting the climate is called radiative forcing*.

Climate change models predict that human activity emits greenhouse gases and affects the Earth's energy balance. This time, NASA's research has confirmed for the first time by actual observation that radiative forcing is increased by human activity, causing climate change through the earth's energy balance. In this study, the researchers calculated the artificial radiative forcing by subtracting natural factors such as water vapor, clouds, temperature, and surface albedo (the brightness or reflectivity of the earth’s surface) from the imbalance of the earth's energy balance. They also found that in 2003-2018, greenhouse gases from power generation, transportation, manufacturing etc. caused radiative forcing of 0.5 watts per square meter. In addition, the method used in this study is faster than previous model-based methods, facilitates monitoring of radiative forcing in real time, and enables more reliable prediction of climate change. 

* According to Wikipedia, radiative forcing is the difference between solar irradiance (sunlight) absorbed by the Earth and energy radiated back to space. It is the scientific basis for the greenhouse effect on planets, and plays an important role in computational models of Earth’s energy balance and climate. 

Reference

NASA. Direct Observations Confirm That Humans Are Throwing Earth's Energy Budget off Balance. By Sofie Bates, NASA’s Earth Science News Team.  March 25, 2021. https://climate.nasa.gov/news/3072/direct-observations-confirm-that-hum…

Contributor: IIYAMA Miyuki (Research Strategy Office)