Abstract
Abstract. Continued anthropogenic greenhouse gas (GHG) emissions are expected to cause further global warming throughout the 21st century. Understanding the role of natural forcings and their influence on global warming is thus of great interest. Here we investigate the impact of a recently proposed 21st century grand solar minimum on atmospheric chemistry and climate using the SOCOL3-MPIOM chemistry–climate model with an interactive ocean element. We examine five model simulations for the period 2000–2199, following the greenhouse gas concentration scenario RCP4.5 and a range of different solar forcings. The reference simulation is forced by perpetual repetition of solar cycle 23 until the year 2199. This reference is compared with grand solar minimum simulations, assuming a strong decline in solar activity of 3.5 and 6.5 W m−2, respectively, that last either until 2199 or recover in the 22nd century. Decreased solar activity by 6.5 W m−2 is found to yield up to a doubling of the GHG-induced stratospheric and mesospheric cooling. Under the grand solar minimum scenario, tropospheric temperatures are also projected to decrease compared to the reference. On the global scale a reduced solar forcing compensates for at most 15 % of the expected greenhouse warming at the end of the 21st and around 25 % at the end of the 22nd century. The regional effects are predicted to be significant, in particular in northern high-latitude winter. In the stratosphere, the reduction of around 15 % of incoming ultraviolet radiation leads to a decrease in ozone production by up to 8 %, which overcompensates for the anticipated ozone increase due to reduced stratospheric temperatures and an acceleration of the Brewer–Dobson circulation. This, in turn, leads to a delay in total ozone column recovery from anthropogenic halogen-induced depletion, with a global ozone recovery to the pre-ozone hole values happening only upon completion of the grand solar minimum.
Highlights
IntroductionThe observed global warming since the pre-industrial period (1850–1900) until the end of the 20th century (1986–2005) is estimated to be around 0.6 ◦C (IPCC, 2013)
Global warming is one of the main societal problems
Should the grand solar minimum persist until the end of the 22nd century, the difference between reference scenario (REF) and strong reduction (SD) would increase to about 0.6 K, which is about 25 % of projected global warming of 2.3 K at the end of the 22nd century compared to the base period (1986–2005)
Summary
The observed global warming since the pre-industrial period (1850–1900) until the end of the 20th century (1986–2005) is estimated to be around 0.6 ◦C (IPCC, 2013). In December 2015, many countries agreed to make an effort to reduce their emissions of GHG into the atmosphere in order to keep the global surface temperature rise below 2 ◦C above pre-industrial levels. This agreement was adopted under the United Nations Framework Convention on Climate Change (UNFCCC), and it is known as the Paris climate agreement. RCP2.6 is the only GHG concentration scenario that limits the global mean surface temperature increase at 2 ◦C at the end of the 21st century (van Vuuren et al, 2011b)
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