Introduction
The greenhouse effect is caused by the presence in the atmosphere of gases capable of absorbing the infrared radiation emitted by the Earth. The increase in their concentration causes a rise in temperature which can have serious consequences on the Earth's climate. All these gases are called “greenhouse gases” or GHGs (Greenhouse gas). According to the most optimistic hypotheses formulated by the scientists of the IPCC (Intergovernmental Panel on Climate Change), the rate of global warming would result in an increase in the earth's average temperature of around 0.4°C per decade.
Conventions on Climate Change
The environmental consequences of these changes have been described by the Working Group on Impacts of the IPCC. Due to the natural variability of the climate, there are great difficulties in establishing whether a certain event, or set of events, can be connected to greenhouse gas emissions from human activities. All this creates uncertainty that often fuels controversy, but as evidence of this concern, since 1990 over 130 governments have deemed it appropriate to engage in an expensive and complex negotiation for the development of a global climate convention. In the Framework Convention on Climate Change in Rio De Janeiro during the “Earth Summit” (June 1992), it was established that the signatory Parties would adopt programs and measures suitable to return by 2000 to the 1990 levels of carbon dioxide emissions or other greenhouse gases. The Convention is operationalized by annual meetings (Conferences of the Parties or COP). In light of this, a brief chronology of the most relevant events from 1990 to present, along with the most important events, will be presented below.
- COP1 (Berlin, 1995): Focused on the drafting of guidelines for the submission of national reports on greenhouse gases and verification methods.
- COP3 (Kyoto, 1997): Produced the Kyoto Protocol, a binding agreement that set targets for reducing greenhouse gas emissions for developed countries.
- COP6 (Bonn, 2001): Focused on negotiations for the implementation of the Kyoto Protocol, including flexible mechanisms such as emissions trading and the Clean Development Mechanism (CDM).
- COP11 (Montreal, 2005): Marked the entry into force of the Kyoto Protocol and addressed issues of adaptation to climate change.
- COP15 (Copenhagen, 2009): Sought to reach a global agreement on climate post-2012, but only resulted in a non-binding agreement known as the Copenhagen Accord.
- COP17 (Durban, 2011): Led to the adoption of the Durban Protocol, which set the basis for a new global climate agreement by 2015.
- COP21 (Paris, 2015): Produced the Paris Agreement, a binding global agreement aimed at limiting the increase in global temperature below 2°C compared to pre-industrial levels, with efforts to limit it to 1.5°C. The Paris Agreement has been ratified by numerous countries.
- COP24 (Katowice, 2018): Established the rules for implementing the Paris Agreement, including transparency, measurement, and financing.
- COP26 (Glasgow, 2021): Focused on accelerating efforts to achieve the goals of the Paris Agreement and on funding for developing countries for climate change adaptation and mitigation.
There have been many other COPs between these, each with its own specific themes and objectives. The complete list of COPs can be found on the official website of the United Nations Framework Convention on Climate Change (UNFCCC).
Quantitative Assessment of the Greenhouse Effect
In quantitative terms, the study of the phenomenon addresses the individual gases responsible for the greenhouse effect, examining their origins and evaluating variations in concentration in the atmosphere. There have always been greenhouse gases in the atmosphere; the main ones are water vapor (the most abundant) and carbon dioxide (second in importance) produced by volcanoes and the natural carbon cycle. While the function of natural greenhouse gases is to allow the Earth's surface temperature to remain within certain values compatible with maintaining life on the planet, those produced by human activities can disrupt natural system balances if their concentration and accumulation rate exceed certain limits. The anthropogenic greenhouse gas that raises the most concern is carbon dioxide, mainly derived from the combustion of fossil fuels. Other gases, to varying degrees, contribute to the greenhouse effect such as methane (CH4), nitrous oxide (N2O), chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and sulfur hexafluoride (SF6). The quantities of analyzed greenhouse gases are generally expressed in kg CO2 equivalents (kgCO2 eq), through a process of standardization based on global warming potentials (GWPs - Global Warming Potentials).
These potentials adopted by the IPCC are calculated for each greenhouse gas considering its radiation absorption capacity and the residence time in the atmosphere. The GWP of a substance is calculated as the ratio between the contribution that the instantaneous release of 1kg of that substance provides to the absorption of heat radiation and that provided by the emission of 1kg of CO2, both contributions evaluated for a period of T years of the gas's presence in the atmosphere (Houghton et al., 1991).
GWPs are evaluated for different exposure periods, defined as “time horizons”: these are usually set at 20, 50, 100, 200, or 500 years. It is customary to refer to GWPs at 100 years (average period), also because as time increases, uncertainties related to the calculation model also increase.
Example: Let's assume we are studying an activity that releases into the atmosphere 1kg of CO2 (GWP 100 = 1kgCOeq) and 1 kg of methane (GWP 100 = 27kgCO2eq); the total emission for the category “Climate change” would be:
E = 1kgCO2 * 1kgCO2eq + 1kgCH4 * 27kgCO2eq = 28 kgCO2 equivalents
