Q&A -Does Human Activity, In Addition To CO2 and Other Human-Added Greenhouse Gases, Significantly Influence Local, Regional And Global Climate On Decadal Time Scales??

The focus of the 2007 IPCC reports (e.g. see) have been to emphasize the annual average top of the atmosphere (TOA) radiative forcing in conjunction with the global average surface temperature trends as the primary overarching metrics of climate change (or “climate disruption” using the new terminology).  In 2005, for example, a broader view point was recommended in

National Research Council, 2005: Radiative forcing of climate change: Expanding the concept and addressing uncertainties. Committee on Radiative Forcing Effects on Climate Change, Climate Research Committee, Board on Atmospheric Sciences and Climate, Division on Earth and Life Studies, The National Academies Press, Washington, D.C., 208 pp

where it is written

“Despite all these advantages, the traditional global mean TOA radiative forcing concept has some important limitations, which have come increasingly to light over the past decade. The concept is inadequate for some forcing agents, such as absorbing aerosols and land-use changes, that may have regional climate impacts much greater than would be predicted from TOA radiative forcing. Also, it diagnoses only one measure of climate change—global mean surface temperature response—while offering little information on regional climate change or precipitation.”

Today’s post asks the question

Does Human Activity, In Addition To CO2 and  Other Human-Added Greenhouse Gases, Significantly Influence Local, Regional and Global Climate On Decadal Time Scales?

1. Local Scales

There is absolute certainty that humans very signficantly affect climate on decadal time scales on the localscale. Urbanization is one particularly obvious effect. As just a few examples that I have posted on, see

New Paper “Contribution Of Land Use Changes To Near-Surface Air Temperatures During Recent Summer Extreme Heat Events In The Phoenix Metropolitan Area” Et Al Grossman-Clarke Et Al 2010

New Paper “The Impact Of Urbanization On Current And Future Coastal Precipitation: A Case Study For Houston” By Shepherd Et Al 2010

New Paper “Global Urban Land-Use Trends And Climate Impacts” By Seto and Marshall 2009

New Paper Accepted “Urbanization Signature In The Observed Heavy Rainfall Climatology Over India” By Kishtawal Et Al 2009

2. Regional Scales

Similarly, on the regional scale, there is ample evidence of a major effect of human activities on multi-decadal climate. Examples, of posts on this include

Sensitivity of Summer Near-Surface Temperatures and Precipitation in the Eastern United States to Historical Land Cover Changes Since European Settlement by Strack et al. 2008

A New Paper That Highlights the First-Order Radiative Forcing Of Black Carbon Deposition

New Paper “Numerical Simulations Of The Impacts Of Land-Cover” By Kala Et Al 2010

Paper ” Evidence Of Enhanced Precipitation Due To Irrigation Over The Great Plains Of The United States” By DeAngelis Et Al 2010

New Paper “Effects Of Irrigation On Global Climate During The 20th Century” By Puma and Cook (2010)

3. Global scale

The 2007 IPCC report takes the view that the annual global averages of the top of the atmosphere radiative forcing and surface temperature trends are the primary metrics. Yet, what is much more important is how planetary atmospheric and oceanic circulations can be altered by human activity. I agree that the addition of CO2 and other greenhouse gases can influence these circulartions. However, as concluded in the 2005 NRC report [highlight added]

“Regional variations in radiative forcing may have important regional and global climatic implications that are not resolved by the concept of global mean radiative forcing. Tropospheric aerosols and landscape changes have particularly heterogeneous forcings. To date, there have been only limited studies of regional radiative forcing and response. Indeed, it is not clear how best to diagnose a regional forcing and response in the observational record; regional forcings can lead to global climate responses, while global forcings can be associated with regional climate responses. Regional diabatic heating can also cause atmospheric teleconnections that influence regional climate thousands of kilometers away from the point of forcing.”

Several types of forcings—most notably aerosols, land-use and land-cover change, and modifications to biogeochemistry—impact the climate system in nonradiative ways, in particular by modifying the hydrological cycle and vegetation dynamics. Aerosols exert a forcing on the hydrological cycle by modifying cloud condensation nuclei, ice nuclei, precipitation efficiency, and the ratio between solar direct and diffuse radiation received. Other nonradiative forcings modify the biological components of the climate system by changing the fluxes of trace gases and heat between vegetation, soils, and the atmosphere and by modifying the amount and types of vegetation. No metrics for quantifying such nonradiative forcings have been accepted. Nonradiative forcings have eventual radiative impacts, so one option would be to quantify these radiative impacts. However, this approach may not convey appropriately the impacts of nonradiative forcings on societally relevant climate variables such as precipitation or ecosystem function.”

Examples of posts that discuss alterations in planetary circulation patterns by human activity include

Further Confirmation Of Hypothesis 2a In Pielke Et Al 2009

News Release On Soot Effects On Climate In The Himalayas – Its Larger Than the Forcing From The Human Input Of CO2

The Importance Of Regonal Climate Forcings

Teleconnections In The Earth System By Chase, Pielke and Avissar

What is the Importance to Climate of Heterogeneous Spatial Trends in Tropospheric Temperatures?

4. Conclusion

In answer to the question,

Does Human Activity, In Addition To CO2 and  Other Human-Added Greenhouse Gases, Significantly Influence Local, Regional and Global Climate On Decadal Time Scales?

the answer is clearly YES. The presentation of views in which CO2 and a few other greenhouse gases dominate the role of humans within the climate system is scientfically incorrect.

The consequences of adopting the narrow, scientifically incomplete view point of the IPCC is, as we concluded in

 Pielke Sr., R., K. Beven, G. Brasseur, J. Calvert, M. Chahine, R. Dickerson, D. Entekhabi, E. Foufoula-Georgiou, H. Gupta, V. Gupta, W. Krajewski, E. Philip Krider, W. K.M. Lau, J. McDonnell,  W. Rossow,  J. Schaake, J. Smith, S. Sorooshian,  and E. Wood, 2009: Climate change: The need to consider human forcings besides greenhouse gases. Eos, Vol. 90, No. 45, 10 November 2009, 413. Copyright (2009) American Geophysical Union

that, by itself,

“a policy that focuses on modulating carbon emissions”

will not provide an effective framework to deal with the spectrum of risks from human (and natural) caused climate variability and change in the future.

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