Limiting global warming by the threshold of 1.5°C: The changing hydrosphere

Hydrosphere-atmosphere interactions play an integral part in the Earth system; for example, 25% of carbon dioxide (CO₂) is absorbed by the ocean alone (Canadell et al., 2007, as cited by Seijo et al., 2016, p.1). Thus water bodies on Earth act as major carbon sinks. However, global warming, caused by exponentially rising anthropogenic carbon emissions, is disrupting the equilibrium of many earth systems, including the hydrosphere. The aim of the 2015 Paris Agreement is to keep global warming below 1.5°C of pre-industrial levels and is important because this temperature is considered a ‘tipping point’ of the Earth system and for humans are irreversible effects. This essay will look into how some hydrosphere reservoirs including the oceans and cryosphere, and hydrologic fluxes are changing, using sources drawn from the 2018 IPCC Special Report.

Oceans

Oceans constitute 97.5% of water reservoirs (Skinner & Murck, 2001), and play a dominant role in hydrosphere processes. Table 1 (Bittermann et al., 2017, p.5), shows that by 2050, a temperature stabilisation of 1.5°C will correspond to a global mean sea level (GMSL) rise of 19cm. In comparison, a 2°C rise in temperature would cause a 24cm rise. By 2150 however, the GMSL rise for 1.5°C and 2°C, is estimated to be 49cm and 67cm respectively, which is 1.4 times the 1.5°C projection. This variation in GMSL emphasises that global warming should be limited to 1.5°C as the initial small differences in GMSL projections increases over time, having significant implications in the future.