Our evolving climate: communicating the effects of climate variability

Our evolving climate is influenced by several factors such as greenhouse gases and solar output, coupled with the inherent variability of the climate system. Natural fluctuations in climate can temporarily mask or enhance the long-term upwards trend in temperatures, and contribute to uncertainty in climate projections, especially on regional scales. Understanding and acknowledging these variations is important for society and policymakers. This article aims to communicate the impacts of natural variability and discuss recent progress in understanding and predicting natural climate fluctuations. This progress offers potential to narrow uncertainty in climate predictions and may aid efficient adaptation to our changing climate. —————————— It is “very likely” that humans have caused most of the warming of the Earth’s climate since the mid-20th century; this was a key conclusion of the 4th Assessment Report (AR4; Solomon et al., 2007) of the Intergovernmental Panel on Climate Change (IPCC). For the UK, 2006 was the warmest year recorded to date, however 1998 remains the warmest year on record for the global average. This has led many to question whether the climate is changing as projected by the IPCC. This article aims to portray and communicate the important role played by natural variability in our evolving climate. Understanding and acknowledging these variations is important for society and policymakers. Much of this variability is chaotic and unpredictable but some significant fraction is potentially predictable, providing an opportunity to narrow the uncertainty in climate predictions of the coming decade. Our evolving climate The Earth’s climate is changing primarily due to two factors – (i) the response to external forcings such as greenhouse gases, solar output and volcanoes, coupled with, (ii) the inherent internal (or natural) variability of the climate system. These natural fluctuations in climate can temporarily mask or enhance any long-term trends to the extent that one year, or even decade, will not necessarily be warmer (or wetter/drier) than the last. On seasonal and annual timescales, the main climate influence on global scales is the El Nino Southern Oscillation (ENSO) phenomenon – the periodic warming and cooling in the Pacific According to the HadCRUT3 global temperatures dataset used by the IPCC (Brohan et al., 2006; also see Fig. 5 later), although other datasets find more recent years to be warmer than 1998.