# Presentation: 209189

## Global Precipitation Measurement for Global Water Cycle Research & NEWS 

*Pierre Morel**University of Maryland/Baltimore County**15 June 2004*

## Projected changes in the “greenhouse gases” (CO2, CH4...) and aerosols are covered in one third of the IPCC report: Climate Change 2001, as if this was the main unresolved issue in climate science.

*How will the global distribution of atmospheric water vapor adjust to changes in Earth's temperature?*

- Actually the greenhouse effect of water vapor is three times as large as that of all other greenhouse gases together. Over
- the ocean, this radiative effect increases by ~ 100 Watts/m2 as surface temperature rises from 25 to 30o C.
- The main science issue of climate change is therefore:

## Greenhouse effect G of atmospheric water vapor as a function ocean surface 

- Greenhouse effect G of atmospheric water vapor as a function ocean surface
- temperature in the Tropical Pacific (25° North to 25 °South).

## Estimated radiative forcings between 1850 and the present

**Estimated radiative forcings between 1850 and the present**
- (from IPCC, *Climate Change 2001*)

## Greenhouse effect G of atmospheric water vapor as a function ocean surface 

- Greenhouse effect G of atmospheric water vapor as a function ocean surface
- temperature in the Tropical Pacific (25° North to 25 °South).
- Radiative forcing by other greenhouse gases and aerosols (from IPCC, *Climate*
*Change 2001*) shown on the same scale for comparison.

## Water vapor largely follows the Clausius -Clapeyron law in the atmospheric boundary layer, but not in the mid- and upper troposphere where it counts most for the greenhouse effect. 

- Water vapor in the “free troposphere” away from the
- boundary layer is far from saturation and is constrained
- primarily by vertical transport, condensation processes,
- and precipitation, i. e. *sink processes, not sources*.

*Realistic simulation of weather processes and precipitation*
*is key to accurate projections of changes in water vapor*
*distribution, atmospheric greenhouse effect, and climate.*
- .

## In 1967, Manabe and Wetherald used a one-dimensional radiative-convective equilibrium model to assess the response of climate to doubling CO2.  

*Model assumptions were:*
*1.  Relative humidity was specified as a function of altitude only*
*2. **	**Cloud amount and optical properties (albedo) were specified in lower, mid-level, and upper troposphere *
*3. **	**Convective adjustment in the troposphere was introduced in the form of a specified constant lapse rate: – 6.5oC/km *

- The authors estimated that doubling carbon dioxide would
- result in global warming  ~ 2.36oC.

## In 2002, the Intergovernmental Panel on Climate Change

- third assessment report  *Climate Change 2001* estimated
- that doubling carbon dioxide would raise global-mean (surface) temperature by 2.9o C  ±  1.3o C.

*	**Climate models used in this exercise featured three-dimensional representations of atmospheric circulation, a full range of energy and water sources or sinks, interactive clouds, and “parametric” representations of water and energy fluxes, cloud processes, condensation and rain. *

- But most of Manabe’s early assumptions were still embedded in these state-of-the-art models, hidden in the parametric representation of water cycle processes.

## <http://www.cgd.ucar.edu/~tls/CSM/tables.html>

- <http://www.cgd.ucar.edu/~tls/CSM/tables.html>

## Slide 10

## Potential changes in the water cycle and rainfall patterns are the most significant among immediate consequences of global warming. 

- A most pressing problem at this stage of climate science is quantifying the predictable consequences of projected global climate change, such as changes in:

-   *The distribution, frequency and intensity of weather   disturbances.  *
*  **The amount and distribution of precipitation. *
*  **The frequency and intensity of severe hydrologic events. *

## GPM will, during the next decade, become the 

- GPM will, during the next decade, become the
-       most significant global observation program
- for advancing the state of the art in climate science and climate change assessment.

- Because

*Understanding precipitation processes and rain is key to quantifying water feedback under different climate conditions, projecting global climate change and assessing hydrologic consequences,*