Chapter 6: Climate Change
The world is getting warmer. Global average temperatures have risen markedly since the mid-20th century and human activities are very probably responsible for much of this increase. Over the past 50 years, the warming of the oceans accounts for more than 80% of the change in the energy content of the Earth’s climate system. In this chapter we look at the implications of this climate change for the marine environment (see Figures 6.1 and 6.2). Although its effects can often be masked by natural changes, we can nonetheless link a wide range of observed changes in the marine environment to the changing climate, either directly through the effects of physical and chemical parameters such as temperature and acidity, or indirectly through impacts on the timing, distribution and abundance of marine species.
Charting Progress did not explicitly evaluate climate change but it did recommend the creation of a Marine Climate Change Impacts Partnership (MCCIP) to act as a mechanism for collating and communicating evidence. For this chapter we have combined material provided by the MCCIP with summaries of the climate-related assessments of the Feeder Reports prepared by the Ocean Processes Evidence Group, the Healthy and Biologically Diverse Seas Evidence Group, the Clean and Safe Seas Evidence Group and the Productive Seas Evidence Group, examining the evidence available for the effects of climate change on the marine environment, ecosystem and activities that rely on the sea.
We have based our assessments of what could happen in the future on both the latest report from the Intergovernmental Panel on Climate Change (IPCC) and on the latest set of climate information, the UK Climate Projections 2009, which were commissioned by the UK Government and published in June 2009. UKCP09 represents a significant advance from its predecessor, UKCIP02. As well as providing atmospheric variables such as mean air temperature, sea level pressure, total cloud and precipitation rate, it also gives extensive information about the ocean surface and sub-surface including projections of sea-level rise, storm surges, multi-level data on water temperatures, salinity and the stability of the water column around the UK, as well as changes in wave height.
While many of the changes we observe are consistent with increasing levels of atmospheric carbon dioxide (CO2) and a warming climate, for example rising sea temperature and increasing acidification, we still do not understand many of the causative links to climate change. In particular we struggle with the rate and magnitude of future change for factors such as sea-level rise, Atlantic circulation, sea-ice extent, acidification and stratification. In other cases, for example the extent to which the oceans will continue to take up CO2, or changes in storminess or salinity, we are not even sure which direction the change in marine climate will take. Finally, some important potential changes such as coastal erosion will be so highly localised that they are difficult to map.
Furthermore, there are often insufficient data to draw robust links between climate change and impacts on marine ecosystems, and in some cases we do not sufficiently understand the underlying effects of climate change on the physical environment. Resolving these problems will be crucial if we are to learn how to mitigate the potential effects of climate change on the marine environment, as well as to adapt to those that are already inevitable.
Figure 6.1 An idealised model of the natural greenhouse effect.