Climate change is being driven primarily by increasing concentrations of long-lived greenhouse gases (GHGs), in our atmosphere. Since the industrial revolution in the mid-19th century, the combustion of fossil fuels has resulted in ever growing carbon dioxide (CO2) emissions while other wide-scale human activities such as intensive agriculture have resulted in growing emissions of methane (CH4) and nitrous oxide (N2O). The figure below shows our 2000 year record of CO2, CH4 and N2O derived from measurements of air trapped in Antarctic ice and firn, and from direct sampling at Cape Grim.
From around the mid-20th century, synthetic GHGs, such as those used for refrigeration have also been growing in the atmosphere. The cumulative effect of these emissions is to trap increasing amounts of heat in the Earth’s atmosphere, known as radiative forcing. To illustrate this, below is the increase in radiative forcing calculated from our Cape Grim and Antarctic (ice core and firn) GHG measurements over the past 100 years. Consequently we now see systematic evidence of a warming climate, with shifts in weather patterns and increases in the frequency of extreme weather events.
The Paris Climate Agreement represents an international response to limit global temperature rise to well below 2˚C, with respect to the pre-industrial climate, by all nations radically curbing their GHG emissions over coming decades. To this end, countries have pledged ‘Nationally Determined Contributions’, setting targets for emissions reduction. Currently, nations report their emissions to the United Nations Framework Convention on Climate Change (UNFCCC) as determined via prescribed ‘bottom-up’, or inventory methods. A complementary approach to determining emissions (so called ‘top-down’) is to use atmospheric concentration measurements in conjunction with a model of atmospheric transport to infer emissions. By using the amount of each GHG present in the atmosphere as a constraint on total emissions estimation, we can determine whether we are on track to meet our obligations under the Paris Agreement. Furthermore, a top-down approach may reveal flaws in bottom-up derived emissions estimates, which can lead to more accurate reporting or point to low-hanging fruit to target in mitigation efforts.
Through our extensive network of measurement sites around Australia and the globe, we generate significant datasets that are used in an inverse modelling framework to provide emissions estimates for a range of GHGs. This top-down or inverse approach can be used at a range of spatial scales, from global, to continental, national, regional or even city scale.
Our CO2, CH4 and N2O data have been used in many global scale inversions to constrain total emissions of these three major GHGs, as well as regional scale emissions estimation. In addition, measurements of a range of synthetic GHGs at Cape Grim have been used to determine Australian emissions estimates of these gases, often highlighting problems with inventory methods. Where discrepancies have been highlighted, we have then worked with the relevant government department responsible for reporting Australia’s emissions to the UNFCCC, to identify the causes of the discrepancies and collaborate with them to improve inventory estimates.