New ACCESS climate simulations from 1850-2005

Researchers within the Centre of Excellence have now completed two more climate simulations using the Australian Community Climate and Earth System Simulator (ACCESS) version 1.3, this time for the period 1850 to 2005 forced with increasing concentrations of greenhouse gases only.

Recently, high priority climate variables were uploaded from ACCESS model simulations to the Earth System Grid for general use. These important climate variables, such as precipitation and surface air temperature, were produced in historical experiments using ACCESS.

The historical simulations are standardised experiments, which were conducted as part of the international CMIP5 effort, and are designed to replicate the climate from 1850-2005 as accurately as possible, using both natural and human-related factors.

The most recently completed ACCESS simulations are part of the CMIP5 detection and attribution set of experiments. In the historical greenhouse gas (historicalGHG) experiment, the model is forced by changing atmospheric composition (including carbon dioxide), but no natural variations occur. 

The primary difference in the climate between the two experiments (historical and historicalGHG) is related to the impact of aerosols. Aerosols are solid or liquid particles suspended in the atmosphere and include sea salt, mineral dust and soot from fossil fuel burning.

Aerosols represent a complex forcing of the climate system, impacting both the energy balance in the atmosphere and the hydrological cycle through clouds. The scattering of incoming solar radiation by aerosols in the atmosphere generally acts to cool the atmosphere.

Aerosols are derived from both industrial activity and from natural sources, such as from the intermittent eruption of volcanoes.

Several large volcanic eruptions occurred in the period 1850-2005, which are evident as rapid cooling in the observational record and the all-forcings simulations (see Figure above).

For example, the eruptions of Mount Pinatubo, in the Philippines in 1991, and Krakatoa, in Indonesia in 1883, can be seen in the global surface temperature record. However, these events are not evident in the greenhouse gas forced climate simulations, which do not include aerosol forcings. 

In addition, global average temperatures in the historical GHG simulations (without aerosols) are notably warmer than the historical simulations using all forcings, including aerosols.  

A third historical simulation with only greenhouse gas forcings is currently being conducted, to compare the set of three, each start with different initial conditions.

We will be using the output from these experiments for a series of analyses comparing climate variables in the all forcings experiments with those using only greenhouse gas forcings.

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