SO&P: ECHO-G Natural and anthropogenic forcing

Important notes regarding the ECHO-G data:

• Do not redistribute data to others outside the SO&P project.
• GKSS or FUB may require co-authorship (depending on the level of their involvement), but they certainly want to be informed about what analyses you are using the ECHO-G data for. Please contact Julie Jones for the erik data or Irina Fast for the enat data (see SO&P participants table) and keep them informed.
• To ensure collaboration between SO&P partners, please refer to the list of ongoing/planned model-data comparisons. Please contact others who have listed an interest in the same area, to initiate collaboration. To add your planned areas of model-data work to the list, email Tim Osborn.
• Climate drift, unrelated to the external forcings, may be present in the ECHO-G simulations. An appropriate ECHO-G control simulation for assessing and removing any drift has not yet been performed. Data users should take this into account when using this data.
• Please inform Tim Osborn of any errors that you find in the data.

In all plots below, the horizontal lines indicates the value used in the ECHO-G present-day control simulation.

ECHO-G Natural forcings

Solar and Volcanic The only time-varying natural forcings used in the ECHO-G simulations are solar irradiance changes and short-wave forcing related to volcanic eruptions. The volcanic forcing is implemented by reducing the effective solar irradiance to achieve the desired effect. This is a simplification which neglects differences in the pattern of volcanic short-wave between eruptions and between volcanoes and solar irradiance variations, and neglects absorption of short-wave and long-wave radiation by volcanic aerosols that can lead to stratospheric warming. The time series shown in the upper panel is the effective solar irradiance used as one of the forcings in the erik simulation, and used after 1756 as the only forcing in the enat simulation. The data files contain separate time series of effective solar irradiance including solar variability and perturbations due to volcanic forcing, which can be summed to yield the time series plotted in the upper panel. The lower panel shows this irradiance time series converted to a forcing time series by Osborn, Raper and Briffa (2005) (see SO&P publications for reprint).

Data Annual solar volcanic

ECHO-G Greenhouse gas forcings

CO2 Time-varying concentrations of carbon dioxide were prescribed in the ECHO-G erik simulation, including some pre-industrial variations which might include a natural component. The upper panel shows the prescribed concentrations, and these are contained in the data file. Osborn, Raper and Briffa (2005) (see SO&P publications for reprint) used IPCC radiative forcing relationships to estimate the radiative forcing time series associated with these CO2 changes, and this forcing is shown in the lower panel.	Data Annual CO2
CH4 Time-varying concentrations of methane were prescribed in the ECHO-G erik simulation, including some pre-industrial variations which might include a natural component. The upper panel shows the prescribed concentrations, and these are contained in the data file. Osborn, Raper and Briffa (2005) (see SO&P publications for reprint) used IPCC radiative forcing relationships to estimate the radiative forcing time series associated with these CH4 changes, and this forcing is shown in the lower panel.	Data Annual CH4
N2O Time-varying concentrations of nitrous oxide were prescribed in the ECHO-G erik simulation. Pre-industrial concentrations were kept constant. The upper panel shows the prescribed concentrations, and these are contained in the data file. Osborn, Raper and Briffa (2005) (see SO&P publications for reprint) used IPCC radiative forcing relationships to estimate the radiative forcing time series associated with these N2O changes, and this forcing is shown in the lower panel.	Data Annual N2O
Total greenhouse gas forcing The radiative forcings estimated by Osborn, Raper and Briffa (2005) (see SO&P publications for reprint) for each of the three greenhouse gases used in ECHO-G erik (CO2, CH4 and N2O) have been summed to yield the total greenhouse gas radiative forcing. This is shown below.

ECHO-G Total of natural and anthropogenic forcings

Total forcing The total greenhouse gas radiative forcing estimated by Osborn, Raper and Briffa (2005) (see SO&P publications for reprint) and the combined solar and volcanic forcing (expressed as a radiative forcing by Osborn, Raper and Briffa, 2005) have been summed to yield an estimate of the total radiative forcing used in the ECHO-G erik simulation. This is shown below.