The impact of solar variability and aerosols on the Earth's climate is believed to be comparable to the impact posed by greenhouse gases.* Still, aerosols remain poorly measured and may represent the largest uncertainty in our understanding of climate changes. The root of the problem is that the Earth's atmosphere and its surface have a complex relationship, which leads to large uncertainties in simulations that scientists use to describe and understand this system. The objective of the Glory mission is to reduce these uncertainties.The mission will also study the formerly so-called "solar constant."
The Sun Factor
The primary input to the Earth's energy balance comes from a natural source: our Sun. To find out the contribution of this giant space heater to the Earth's energy budget, scientists will measure the amount of energy that reaches the Earth's atmosphere over a given period of time. The current estimate is approximately 1,361 watts per square meter. That's enough energy incident on the Earth to continuously power nearly half a million 60-watt light bulbs per person. Previous sensors have provided a data record spanning the past 30 years, but these measurements of solar intensity contain slight offsets. That's one reason why scientists must maintain a continuous solar measurement record; Glory will provide continuity of this measurement.
Energy from the Sun fluctuates depending on solar changes, such as sunspots, which peak in number with an 11-year average period. While it is easy to recognize that the Sun contributes to the "heat in" portion of the Earth's energy budget, it is not so simple to account for the subtle changes in the Sun's intensity in this budget analysis. The data from the instruments on Glory will help to answer some of these questions.
The Sun provides heat to our planet. However, only about half of the sunlight heats the surface of the Earth. A third of the sunlight is reflected back into space by the surface and atmosphere, while one sixth is absorbed in the atmosphere and then re-emitted. This energy budget of "heat in" versus "heat out" directly influences the Earth's short-term and long-term climate trends.
An accurate description of Earth's energy budget is important for scientists in order to anticipate future changes to our climate. Shifts in the global climate and the associated weather patterns impact human life by altering landscapes and changing the availability of natural resources. Scientists are actively working to better understand exactly how and why this energy budget changes. The NASA Goddard Space Flight Center (GSFC) Glory mission will provide significant contributions toward this critical endeavor.
Glory: Explaining the Earth's Energy Budget
Scientists who study the Earth's energy balance consider the difference between energy entering and energy leaving the lowest layer of Earth's atmosphere (generally, energy entering has a warming effect while energy leaving has a cooling effect).
Specifically, the Glory mission is intended to meet the following two scientific objectives:
Measure solar energy entering the Earth's atmosphere to determine its long-term effects on the Earth's climate record
Collect data on the properties of natural and human-caused aerosols in the Earth's atmosphere
A second factor affecting the Earth's energy balance is the influence of aerosols, which are tiny particles suspended in the atmosphere. Aerosols come from both natural sources such as volcanoes, fires and desert dust, and from human sources, such as the burning of fossil fuels. Aerosols impact the Earth's energy balance by either absorbing or reflecting solar energy. Black carbon aerosols, for example, absorb the heat and then re-radiate some of that energy, contributing to more "heat in." Non-absorbing aerosols, such as sulfates, reflect the Sun's energy back into space causing cooling, or "heat out." In addition, aerosols also indirectly impact atmospheric cooling by changing the properties of clouds and altering precipitation patterns.
Both natural and human-caused aerosols have an impact on global temperatures. Over the past century, the average temperature of the Earth has increased by approximately 1.3 degrees F (0.7 degrees C). Accurately attributing this increase and the accompanying climate change to natural events, human sources, or a combination of both is of primary importance to scientists and policy makers. The aerosol sensor on Glory will provide scientists with accurate measurements of aerosols in our atmosphere and will help scientists better understand how they influence the climate.
The impact of solar variability and aerosols on the Earth's climate is believed to be comparable to the impact posed by greenhouse gases. Still, aerosols remain poorly measured and may represent the largest uncertainty in our understanding of climate changes. The root of the problem is that the Earth's atmosphere and its surface have a complex relationship, which leads to large uncertainties in simulations that scientists use to describe and understand this system. The objective of the Glory mission is to reduce these uncertainties.
*that's not what the IPCC table of radiative forcing components says: According to the IPCC, greenhouse gases create 2.64 Wm-2 positive forcing and aerosols + solar irradiance net to -1.08 Wm-2 (a net negative forcing) of 41% of the claimed GHG magnitude.