Measuring how climate models calculate the effects of clouds on Earth's warming

Mar 06, 2012
Clouds get in the way of the dawn light, perfectly framing the Raman lidar instrument at the ARM Climate Research Facility Southern Great Plains site. This ground-based laser is a remote sensing instrument used for measuring vertical profiles of several cloud and atmospheric properties.

Using ten years of data gathered at three unique measurement sites, scientists at Pacific Northwest National Laboratory and Lawrence Livermore National Laboratory found that global climate models are not representing just how much clouds mask the sun's warming energy. And for the first time, scientists used data on the spatial coverage, height, and transparency of the clouds to inform climate models. They found the relative monthly and annual differences among three cloud fraction datasets at each site are small. However, comparing observations with a dozen global models shows that cloud coverage is significantly misrepresented in the models, by up to 150 percent at one site.

Ever stood under the shadow of a cloud on a sunny day? Then you already know that the amount of clouds covering the Earth is a primary factor on the warming or cooling of the surface. The sun's energy, or , is the primary source of Earth's warming. But clouds get in the way, changing the amount of energy reaching the Earth's surface. Scientists want to know just how much energy is reaching the surface and how much is reflected away or absorbed by clouds. Getting an of clouds, or how much surface they shade at any one time, called cloud fraction, will help scientists predict how and where clouds influence Earth's warming and cooling. Beyond warmth and cooling, getting an accurate picture of will impact predictions of precipitation and air quality around the world.

"Everyone agrees that clouds are the most uncertain agent for prediction in . That's why the U.S. Department of Energy has made a substantial investment in collecting cloud and radiation ," said Dr. Yun Qian, and principal investigator on the study. "In our study, we have taken the raw data and showed how it's ultimately valuable for evaluating cloud fraction, height, and their radiative effect. We then compared this data with a collection of climate models to answer the questions, ‘Where should you pay more attention?' and ‘How well do current global models include clouds and cloud fraction?'"

Researchers gathered data from three Atmospheric Radiation Measurement (ARM) Facility locations: North Slope of Alaska, Southern Great Plains (in Oklahoma), and Tropical Western Pacific. These represent the broad range of climate conditions around the world. The locations each house large groups of atmospheric instruments. Data for this study were gathered by instruments that measured cloud fraction, such as the total sky imager (TSI) which captures a hemispheric view of cloud cover during daylight hours, radar and lidar, used to measure cloud depth and height in one vertical location, and radiometers that measure the shortwave and longwave radiative fluxes.

These data sets were compared among each other at each site to gain insight on how closely the different measurements of cloud fraction are correlated with each other. The inter-comparison revealed relative small monthly and annual differences among the three datasets within each site. The observational data was then compared to cloud fraction representations in a set of 12 global circulation models (GCMs) used in the Intergovernmental Panel of Climate Change (IPCC) reports. Scientists were interested in determining the inter-model deviation and model bias against observation. In addition, they diagnosed potential differences among the GCMs in other cloud optical properties, including cloud transparency, height, and density. They found that the climate models tend to have larger discrepancies from observations for the cloud variables that also have larger inter-model differences.

The cloud fraction varied at different heights, which has a different heating effect changing the overall climate circulation. Researchers have gained new insight on ways to improve the prediction of in .

Using the ARM cloud and radiation data together with satellite data, scientists at PNNL will be working on the prediction of cloud properties in CAM5, the newest version of the Community Atmosphere Model, a global atmospheric process model.

"This research will spark improvements for each global model on how to use the ARM cloud fraction data," said Qian.

Explore further: Clean air: Fewer sources for self-cleaning

More information: Qian Y, et al. 2012. "Evaluation of Cloud Fraction and Its Radiative Effect Simulated by IPCC AR4 Global Models Against ARM Surface Observations," Atmospheric Chemistry and Physics, 12, 1785-1810. DOI:10.5194/acp-12-1785-2012

add to favorites email to friend print save as pdf

Related Stories

Predicting Arctic sea ice loss

Jan 17, 2012

(PhysOrg.com) -- Arctic clouds are strongly tied to Arctic sea ice loss. To find the strength of those ties, a team led by scientists at Pacific Northwest National Laboratory tested a prominent climate model ...

New tool clears the air on cloud simulations

Oct 26, 2011

(PhysOrg.com) -- Climate models have a hard time representing clouds accurately because they lack the spatial resolution necessary to accurately simulate the billowy air masses.

Down-and-dirty details of climate modeling

May 04, 2011

For the first time, researchers have developed a comprehensive approach to look at aerosols—those fine particles found in pollution—and their effect on clouds and climate. Scientists from Pacific ...

The proof is in the clouds

Jan 26, 2012

For most people, clouds are just an indication of whether it's a "good" or "bad" day. A team of scientists from Pacific Northwest National Laboratory found that certain clouds hold the key to climate behavior ...

The insides of clouds may be the key to climate change

Feb 17, 2007

As climate change scientists develop ever more sophisticated climate models to project an expected path of temperature change, it is becoming increasingly important to include the effects of aerosols on clouds, according ...

Recommended for you

Clean air: Fewer sources for self-cleaning

7 hours ago

Up to now, HONO, also known as nitrous acid, was considered one of the most important sources of hydroxyl radicals (OH), which are regarded as the detergent of the atmosphere, allowing the air to clean itself. ...

There's something ancient in the icebox

7 hours ago

Glaciers are commonly thought to work like a belt sander. As they move over the land they scrape off everything—vegetation, soil, and even the top layer of bedrock. So scientists were greatly surprised ...

Image: Grand Canyon geology lessons on view

14 hours ago

The Grand Canyon in northern Arizona is a favorite for astronauts shooting photos from the International Space Station, as well as one of the best-known tourist attractions in the world. The steep walls of ...

First radar vision for Copernicus

14 hours ago

Launched on 3 April, ESA's Sentinel-1A satellite has already delivered its first radar images of Earth. They offer a tantalising glimpse of the kind of operational imagery that this new mission will provide ...

User comments : 0

More news stories

There's something ancient in the icebox

Glaciers are commonly thought to work like a belt sander. As they move over the land they scrape off everything—vegetation, soil, and even the top layer of bedrock. So scientists were greatly surprised ...

Clean air: Fewer sources for self-cleaning

Up to now, HONO, also known as nitrous acid, was considered one of the most important sources of hydroxyl radicals (OH), which are regarded as the detergent of the atmosphere, allowing the air to clean itself. ...

China says massive area of its soil polluted

A huge area of China's soil covering more than twice the size of Spain is estimated to be polluted, the government said Thursday, announcing findings of a survey previously kept secret.

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...