Figure : radiative-forcing

Human Activities Are the Primary Driver of Recent Global Temperature Rise

Figure -.2

University of Washington Seattle
Sarah Doherty

This figure appears in chapter executive-summary of the Climate Science Special Report: The Fourth National Climate Assessment: Volume I report.

Global annual average radiative forcing change from 1750 to 2011 due to human activities, changes in total solar irradiance, and volcanic emissions. Black bars indicate the uncertainty in each. Radiative forcing is a measure of the influence a factor (such as greenhouse gas emissions) has in changing the global balance of incoming and outgoing energy. Radiative forcings greater than zero (positive forcings) produce climate warming; forcings less than zero (negative forcings) produce climate cooling. Over this time period, solar forcing has oscillated on approximately an 11-year cycle between −0.11 and +0.19 W/m2. Radiative forcing due to volcanic emissions is always negative (cooling) and can be very large immediately following significant eruptions but is short-lived. Over the industrial era, the largest volcanic forcing followed the eruption of Mt. Tambora in 1815 (−11.6 W/m2). This forcing declined to −4.5 W/m2 in 1816, and to near-zero by 1820. Forcing due to human activities, in contrast, has becoming increasingly positive (warming) since about 1870, and has grown at an accelerated rate since about 1970. There are also natural variations in temperature and other climate variables which operate on annual to decadal time-scales. This natural variability contributes very little to climate trends over decades and longer. Simplified from Figure 2.6 in Chapter 2. See Chapter 2 for more details.

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This figure was created on June 07, 2017.

This figure was submitted on August 30, 2017.


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