Factors influencing the Region’s values
A number of climate change variables are already changing and, based on a combination of global and regional climate models and observations, are projected to alter substantially in the Great Barrier Reef over the next 50 years.31,32,33,34 It is likely that climate change will drive global changes in prominent weather characteristics and events such as cyclones, heavy rainfall, droughts, air temperature and prevailing winds.31,35,36 For example, while cyclones and other extreme weather events are a natural part of the weather cycle in tropical areas (see Section 3.2.2), the global climate system is now warmer and moister than it was 50 years ago, and this is increasing the chances of intense weather events.37,38 Concentrations of carbon dioxide have increased by 40 per cent since 1750, primarily from fossil fuel emissions and secondarily as a result of changes in land use.39,40 The mean rates of increase in atmospheric concentrations of carbon dioxide, methane and nitrous oxide over the past century are unprecedented in the last 22,000 years, and are now at concentrations unprecedented in at least the last 800,000 years.40 Over the last five years, global carbon dioxide levels have continued to increase at a rate similar to that of the last 50 years, increasing from 386 to 397 parts per million from July 2008 to December 2013 (Figure 6.5).41 Four representative concentration pathways (RCPs) for atmospheric greenhouse gases were developed for use in the fifth assessment report of the Intergovernmental Panel on Climate Change. Of these, the RCP 4.5 represents a ‘radiative forcing is stabilised before 2100’ scenario and RCP 8.5 represents a ‘radiative forcing is stabilised after 2100’ (very high emissions) scenario.31,42 Projections indicate carbon dioxide levels of around 435 (RCP 4.5) to 758 (RCP 8.5) parts per million by 2030, and around 531 (RCP 4.5) and 758 (RCP 8.5) by 2080.43 More than half the observed increase of 0.6 degrees Celsius in global mean surface (air) temperature from 1951 to 2010 is very likely due to anthropogenic greenhouse gas emissions; it is likely that anthropogenic influence has made a substantial contribution to surface temperature increases over Australia.44 Globally, each of the past three decades has been significantly warmer than all the previous decades in the instrumental record and the first decade of the twenty-first century has been the warmest.39 Regionally, mean temperatures are increasing. Projections based on RCP 4.5 and RCP 8.5 suggest temperature will rise by around one to two degrees Celsius by 2030, and by one to over three degrees by 2080.34,44
The ocean is already getting warmer and pH is decreasing.