Climate change

CONSIDERATIONS:

The greenhouse effect is a natural process that heats the Earth’s surface and helps maintain the temperatures suitable for life on the planet, allowing the natural regulation of different water states – most importantly, water in its liquid state that allows life to thrive.

When the sun’s energy reaches the Earth’s atmosphere, some of it is reflected back into space whilst the rest is absorbed and diffused by greenhouse gases that include water vapour, carbon dioxide, methane, nitrous oxide, ozone and, since the intervention of mankind, various artificial chemicals such as chlorofluorocarbons or CFCs. This process, known as ‘the greenhouse effect’, has driven the Earth’s temperature up to be around 33ºC warmer than it would with the total absence of greenhouse gases. Had the predominant sources that contribute to CO₂ concentration in the atmosphere remained the natural ones – respiration, decomposition and volcanic eruption – the mean surface temperature of the planet would have stayed within pre-industrial historical ranges. The increase in the concentration of greenhouse gases due to human activity such as burning fossil fuels – coal, oil and natural gas – as well as agriculture and land cleaning has enhanced the greenhouse effect, heating the Earth to a level that has already disrupted many of its systems’ balances.

In 1992, the United Nations Framework Convention on Climate Change (UNFCCC) created as an objective the stabilisation of greenhouse gas concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with climate systems. Article 2 of that document attests that “such a level should be achieved within a time-frame sufficient to allow ecosystems to adapt naturally to climate change, to ensure that food production is not threatened and to enable economic development to proceed in a sustainable manner”.

Those goals, as we know, were not reached. During COP21, the 21^st Conference of Parties of the UNFCCC in April 2016, the Intergovernmental Panel on Climate Change (IPCC) was invited to produce a special report on what the impact of global warming would be if temperatures rose a further 1.5^oC above pre-industrial levels, and were maintained or capped at this overall temperature for the rest of the century. In this report, released in October 2018, it became clear that anthropogenic emissions have already heated the overall mean temperature of the planet by 1ºC, the effects of which are adverse, will persist for centuries and even millennia, and will continue to cause further, imminent and long-term changes in the climate system. The shift from framing this matter as ‘climate change’ to ‘global warming’ put a subtle but important emphasis on mankind’s actions, addressing not only emissions but also ecosystem degradation, which is a leading emission source in itself. In fact, among emissions caused by humankind, the loss and degradation of natural ecosystems was estimated to have contributed to at least 20 to 30% of the total anthropogenic emissions in 2009, accounting for the equivalent of two to three times the volume of CO₂ emitted by the global transport sector at the time.

The main principles for understanding global warming, listed on session A of the IPCC report, are:

• Human activities are estimated to have caused approximately 1.0ºC of global warming above pre-industrial levels. Global warming is likely to reach 1.5ºC between 2030 and 2052 if it continues to increase at the current rate.
• Estimated anthropogenic global warming is currently increasing at 0.2ºC per decade due to past and ongoing emissions.
• Warming greater than the global annual average is being experienced in many land regions and seasons, including two to three times higher in the Artic. Warming is generally higher over land than over the ocean.
• Trends in intensity and frequency of some climate and weather extremes have been detected over time spans during which about 5^ºC of global warming occurred.
• Warming from anthropogenic emissions will persist for centuries to millennia and will continue to cause further long-term changes in the climate system, such as sea level rise, with associated impacts.
• Impacts on natural and human systems from global warming have already been observed. Many land and ocean ecosystems and some of the services they provide have already changed due to global warming.
• Future climate-related risks depend on the rate, peak and duration of warming. In general, they’ll be larger if global warming exceeds 1.5ºC before returning to that level by 2100 than if global warming gradually stabilizes at 1.5ºC, especially if that peak temperature reaches, for example, around a 2^ºC mean temperature increase. Some impacts may be long-lasting or irreversible, such as the loss of ecosystems.
• On longer time scales, sustained net negative global anthropogenic CO₂ emissions and/or further reduction in non-CO2 radiative forcing may still be required to prevent further warming due to Earth system feedbacks and to reverse ocean acidification, and will be required to minimize sea level rise.

In 2005 The Royal Society of London published a policy document on ocean acidification caused by increasing atmospheric carbon dioxide. Reduction of CO₂ emissions was recommended then to avoid risks of irreversible damage to ocean chemistry and marine ecosystems.

Impacts on natural and human systems from global warming have already been observed. Many land and ocean ecosystems, including the various engagements they provide for mankind, have already changed due to global warming. Governmental policy has, so far, not done nearly enough to put the brakes on ecosystem degradation and climate change at the speed that is needed. The motivation for aligning our activities to benefit the health of natural systems, respecting their limits for resilience, needs to come from us, now, more than ever. Each of us, in each of our own lives, is responsible for the global climate.

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VOCABULARY

(as defined in the United Nations Framework Convention on Climate Change – UNFCCC, 1992)

> CLIMATE CHANGE: A change in climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods

> ADVERSE EFFECTS OF CLIMATE CHANGE: A change in the physical environment or biota resulting from climate change which have significant deleterious effects on the composition, resilience or productivity of natural and managed ecosystems or on the operation of socio-economic systems or on human health and welfare.

> CLIMATE SYSTEM: The totality of the atmosphere, hydrosphere, biosphere and geosphere and their interactions.

> GREENHOUSE GASES: Those gaseous constituents of the atmosphere, both natural and anthropogenic, that absorb and re-emit infrared radiation.

> EMISSIONS: The release of greenhouse gases and/or their precursors into the atmosphere over a specified area and period of time.

> CARBON RESERVOIR: A component or components of the climate system where the carbon is stored.

> CARBON SINK: Any process, activity or mechanism which removes from the atmosphere a greenhouse gas, an aerosol or a precursor of a greenhouse gas, keeping the carbon that once formed these gases stored in a carbon reservoir for a considerable period of time.

> CARBON SOURCE: Any process or activity which releases a greenhouse gas, an aerosol or a precursor of a greenhouse gas into the atmosphere.