Abstract
The observed early 20th century warming (1910 – 1940) is one of the most intriguing and less understood climate anomalies in the twentieth century. To investigate the contributions of natural and anthropogenic factors to the surface temperature changes, we performed seven model experiments using the chemistry-climate model with interactive ocean SOCOL3-MPIOM. Contributions of energetic particle precipitation, heavily (shortwave UV) and weakly (longwave UV, visible and infrared) absorbed solar irradiances, well-mixed greenhouse gases, tropospheric ozone precursors and volcanic eruptions were considered separately. Model results suggest only about 0.3 K of global and annual mean warming during the considered 1910-1940 period which is by about 25% smaller than the trend obtained from observations. We found that the half of the simulated global warming is caused by the well-mixed greenhouse gases (WMGHG: CO2, CH4 and N2O) increase, while the increase of the weakly absorbed solar irradiance is responsible for approximately one third of the total warming. Because the WMGHG behavior is well constrained only higher solar forcing or including new forcing mechanisms can help to reach better agreement with observations. The other considered forcing agents (heavily absorbed UV, energetic particles, volcanic eruptions and tropospheric ozone precursors) contribute less than 20% to the annual and global mean warming, however they can be important on regional/seasonal scales.
Highlights
Two of the strongest global warming periods occurred in the 20th century: 1925–1944 with a temperature increase of 0.37 K and 1978–1997 with a global mean temperature increase of more than 0.32 K (Jones et al, 1999)
The recent advances in climate models and the knowledge of forcing factors motivated us to reevaluate the contributions of natural and anthropogenic factors to early 20th century warming. We address this problem by using our atmosphereocean chemistry-climate model SOCOL-MPIOM (Muthers et al, 2014) driven by different combinations of climate forcing agents to distinguish between the so-called “top-down” and “bottomup” mechanisms of solar influence on climate (Gray et al, 2010)
We used the state of the art chemistry-climate model SOCOL3MPIOM (Stenke et al, 2013; Muthers et al, 2014), which consists of the atmospheric component ECHAM5.4 (Roeckner et al, 2003), the chemistry module MEZON (Rozanov et al, 1999; Egorova et al, 2003), and the interactive ocean module MPIOM (Marsland et al, 2003; Jungclaus et al, 2006)
Summary
Two of the strongest global warming periods occurred in the 20th century: 1925–1944 with a temperature increase of 0.37 K and 1978–1997 with a global mean temperature increase of more than 0.32 K (Jones et al, 1999). The former event has been coined as Early Twentieth Century Warming or ETCW. The rising trend of solar activity (Solanki et al, 2013) could have some influence on the surface temperature. Large volcanic eruptions inject sulfur gases into the stratosphere, which on conversion to sulfate aerosols can scatter solar radiation back into space and cool down the Earth’s surface
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