Brasil Pack Trends 2020

BrasilPackTrends2020 177 sustainabi l ity & ethics FIGURE 7.2 Atmospheric concentrations The changes in the atmospheric concentrations of greenhouse gases and aerosols, land cover and solar radiation alter the energy balance of the climate system and are considered drivers of the climate change. The greenhouse gas change affects the scattering, absorption and emission of radiation within the atmosphere and at the Earth’s surface. The resulting positive or negative changes in energy balance due to these factors are expressed as “radiative forcing”, which is used to compare warming or cooling influences on global climate. Human activities produce mainly four types of long-life greenhouse gases: carbon dioxide (CO 2 ), methane (CH 4 ), nitrous oxide (N 2 O), and halocarbons (a group of gases that contain fluorine, chlorine and bromine). The global atmospheric concentrations of CO 2 and CH 4 in 2005 exceed by far the natural range over the previous 650,000 years (FIGURE 7.2). The increase of the CO 2 concentration is mainly due to the use of fossil fuels and, at a lower scale, due to land-use change. It is very likely that the increase of the CH 4 concentration is predominantly due to agriculture and fossil fuel use. The increase in N 2 O concentration is mainly due to agriculture. The 4 th IPCC report also concluded that the observed changes since the second half of the 20 th century are very likely due to the observed increase of greenhouse gases by anthropogenic action, as shown in Figure 7.3. The warming of the atmosphere and oceans observed on a large scale, together with the loss of ice mass, support the conclusion that it is extremely unlikely that the global climate change of the last 50 years can be explained without external forcing and very likely that it is not due to known natural causes alone. Climate changes causes Atmospheric concentrations of CO 2 , CH 4 and N 2 O over the last 10,000 years (large graphs) and since 1750 (small graphs). Measurements have been performed on ice cores (symbols with different colors for different studies) and atmospheric samples (red lines). The values corresponding to radiative forcings are shown on the right hand axes of the large graphs. Source: IPCC, 2007