What are the spatial and temporal characteristics of natural climate variability?

The climate system exhibits internal variability on a broad range of timescales. However, the observational record is short, and the understanding of climate variability on decadal timescales and longer is therefore limited.

The detection and attribution of anthropogenic climate change requires a complete understanding of the spatial and temporal characteristics of natural climate variability. Furthermore, without such an understanding, we are not able to evaluate the ability of climate models to simulate past and present variability. This limits our confidence in the ability of the models to simulate future climate variability and change.

A critical focus of Earth system research over the coming decade should therefore be on combining observational and palaeoclimatic data to reconstruct natural climate variability over recent centuries and millennia.

How is interdecadal-to-centennial natural variability taken into account in the IPCC GCMs projections?

This low-frequency natural variability might hide or intensify the climate system response to increased greenhouse gases in the atmosphere. In fact, for the next 30 years it seems that interdecadal natural variability would play a major role in the expected changes of rainfall and temperature in many regions, for instance, in South America.

What is the interannual variability in the hydrological cycle over rainfed agriculture areas?

Most of our food is produced from the rainfed areas. Disturbing the existing system could cause great frustrations to the growers, and possible food deficiencies in the future.

How far is the earth system away from its natural variability due to anthropogenic factors?

When we talk about the impact of human activities upon the earth system, we must be sure what is the background of the natural varibilities. We already know throughout the earth history, the earth system has been changing without human being. It is critical for us to know what is the extent of human factor over the natural factors before we talk about further issues.

How is the climate changing and why?

The global mean temperature in 2008 was the lowest since about 2000. Given that there is continual heating of the planet, referred to as radiative forcing, by accelerating increases of carbon dioxide and other greenhouses due to human activities, why isn’t the temperature continuing to go up? The stock answer is that natural variability plays a key role and there was a major La Niña event early in 2008, but this does not answer the question of where the energy has gone. Was it compensated for temporarily by changes in clouds or aerosols, or other changes in atmospheric circulation that allowed more radiation to escape to space? Was it because a lot of heat went into melting Arctic sea ice or parts of Greenland and Antarctica, and other glaciers? Was it because the heat was buried in the ocean and sequestered, perhaps well below the surface? Was it because the La Niña led to a change in tropical ocean currents and rearranged the configuration of ocean heat? Perhaps all of these things are going on? It turns out we can’t answer these definitively. Observations and attribution studies are inadequate. Has global warming really slowed or not?

How will natural and human controls on the atmospheric CO2 concentration operate under the influence of changing climate and changing society in the next 100 years?

We can budget the sources and sinks for carbon for the past 30 years, with increasing confidence over time (Global Carbon Project, 2009). However, we do not have a solid understanding of the mechanisms responsible for variability and change in the natural sinks; nor for potentially dramatic releases of CO2 from permafrost or methane clathrates. We have even less understanding of the societal controls on the CO2 source (beyond a basic need for energy), and thus we do not have a good basis to predict or to control emissions.