The climate of our planet is divided into two great “eras” or “ages”: the glacial (with ice on the surface) and the interglacial (without ice on the surface).
About 15,000 years ago, Earth warmed to the point of melting the ice and sea levels all around the world began to rise.
Since the end of the Ice Age, Earth’s temperature has increased around 16 °F (Fahrenheit Scale—on this scale, the melting point of the water is 32°F and the boiling point is 212°F). Sea levels rose 300 feet and forests began to appear where there was only ice before.
These ice age cycles initiate by subtle changes in the Earth’s orbit around the Sun. These changes slowly alter the amount of solar radiation that reaches different latitudes during slow cycles, which last tens of thousands of years. The Northern ice sheets respond to these changes in summer radiation from high latitudes. When the summer Sun is stronger, snow and ice melt; when it weakens, snow and ice accumulate. (RUDDIMAN, p.2).
Even experiencing several ice ages, the Earth did not freeze, however, these overly cold periods, begun about 2.6 million years ago, triggered the formation of large and thick ice sheets in some parts of the Arctic. The larger and thicker ice sheets got concentrated in Eastern Canada.
The last four ice age cycles in North America lasted about 100,000 years each. However, between each ice season, there was a hot season that lasted about 10,000 years. Thus, the ice ages lasted, on average, 90,000 years. The ice sheet gradually increased during each cold period, until reaching a fairly large size, and then suddenly retreated and disappeared.
Some scientists began studying the phenomenon over a long period of time to understand the causes. Milutin Milanković, a Serbian scientist, observed that the pattern emerged linked to changes in the earth’s orbit around the sun. Thereafter, scientists recognized the importance of orbital characteristics in long-term changes in climate, among other causes.
The greenhouse effect is a natural warming phenomenon of the earth that keeps the temperature of the planet in suitable conditions for the survival of living beings. The sun’s rays reach the atmosphere and greenhouse gases absorb part of its heat (about 50%), and the other part is radiated back to the earth’s surface; this phenomenon keeps the planet warm. In recent decades, the release of greenhouse gases has increased considerably and, with this accumulation of gases, more heat is retained in the atmosphere, which results in a considerable increase in temperature.
All human actions in nature tend to contribute to the destabilization of the greenhouse effect, such as deforestation, use of certain fertilizers, burning of fossil fuels, among others, as they raise the levels of greenhouse gases in the atmosphere and cause a phenomenon known as “global warming.”
And what are the consequences of global warming? Sea levels rising, microorganisms (phytoplankton) that produce oxygen decreasing, imbalance of ecosystems causing the destruction of marine habitats, deserts and climate catastrophes (floods, cyclones, typhoons, hurricanes) increasing, large heat waves, and falling food production are among the most important ones.
The disturbing issue of global warming and greenhouse effect has been provoking several speculations about human participation in the process for decades.
Ruddiman’s work (2015) is based on a scientific debate that has been going on for more than a decade about the great human effects on Earth’s environment and climate: if they began about 150 years ago, with the increase in greenhouse gases emission during the Industrial Revolution, or appeared as part of the Neolithic Agricultural Revolution that followed the discovery and spread of agriculture, thousands of years before.
During most of the evolution of the human species on the planet, men have always sought food in nature, in both flora and fauna, gathering fruits and seeds, tubers and roots, or hunting animals and fishing. Nomadic life imposed some uncertainties about gathering and hunting. A new way of subsistence arose about 10,000 years ago when men began to stay most of the time in a particular place, growing vegetables and herding animals. From this moment on, agriculture started developing and taking different forms throughout the centuries. According to Ruddiman (2015, p. 343), “In a few thousand years, most of the peoples of the earth had become peasants and, over time, urban civilizations began to emerge in several areas.”
The increases in CO2 and CH4 coincided with the time when agriculture was spreading across the earth, which raises the hypothesis that it has played a relevant role in increasing the concentrations of these greenhouse gases. The scientific explanation is that the deforestation to create new pastures or to catch more light to grow the crops emitted CO2 in the atmosphere, and the irrigation of rice paddies, the herding, and the burning of grasses and agricultural residues emitted CH4 in excess.
However, some studies consider these effects irrelevant when compared to the deforestation in the so-called “Industrial Age.”
Models that simulate the use of the earth in the past were created, but these simulations may leave out some historical aspects that show that Chinese and European peasants used much more land per person for 2,000 years than in the following centuries considered pre-industrial. More recent models point out a much greater deforestation and higher CO2 emissions in the Pre-industrial Age. These new studies show that there was an almost total deforestation in Europe, China and India long before the Industrial Age.
The ongoing discussion on natural versus anthropogenic influence on land use, greenhouse gases, and climate in recent millennia proposes two radically different views on the prehistory and history of our species. Either human civilization developed over thousands of years on a planet favored by the warming of a natural interglacial, or, as I believe, we played a significant role in producing a part of the interglacial heat in which our civilizations took shape. (RUDDIMAN, p. 350).
James Hansen, assisted by his colleagues at NASA Goddard Institute for Space Studies, in Manhattan, headed probably the most famous computer program for weather observation. Around 1970, NASA used an initial version of the model to assess the accuracy of forecasts from meteorological observation satellites. The group from the Goddard Institute moved to Washington, but James, who stayed in New York, decided to test the model for predicting climate problems in opposition to the weather. In the following years, the program improved and, although it remains an approximate simulation of the real world, because of its rather complex features, it was possible to predict the effects of increased carbon dioxide and the cumulative effects over time for the year 2,000 and beyond.
According to McKibben (1990, p. 31), there is an infinite number of possible consequences as a result of the temperature change, as for example, seas might rise two meters or more as polar ice melts and warmer water expands, while continents might begin to dry out due to increasing evaporation. Despite this statement, the author considered premature any speculation regarding these effects.
The scale of this uncertainty is so enormous that there are even those who foresee the greenhouse atmosphere yielding an ice age. This theory, formulated by John Hamaker, a retired Midwest engineer, and fervently advanced by a number of California disciples, is dismissed by most professional atmospheric scientists, but it gives an interesting sense of the fragility of present arrangements. (McKibben, 1990, p. 107).
Hamaker believed that the changes in carbon dioxide concentration caused the cycle of glacial periods on Earth in recent geological epochs as a consequence of soil mineralization and demineralization:
Vegetables use soil nutrients – they begin to languish and cause a massive increase of carbon dioxide in the atmosphere – the greenhouse effect heats the equator and causes a large evaporation of tropical waters – the currents of the earth push clouds with water to the north, where they cool and lose moisture – clouds turn into snow – snow forms huge glaciers for the next glacial period – glaciers move through higher latitudes, “scrape” the dirt off the mountains, and “remineralize” the soil – the plants return and the cycle starts again.
Even today, science is not able to forecast how humans would feel facing quite high temperatures during the summers of extreme heat that might become a reality over time.
...all these various changes may be happening at once: it’s hotter and it’s drier and the sea-level is rising as fast as food prices, and the hurricanes are strengthening, and so on. And not the least of it is the simple fact of daily life in a hotter climate. (McKibben, 1990, p. 125).
The use of existing technologies associated with public policies can probably develop solutions based on both scientific and technological searches and the application of laws, decrees and ordinances that regulate energy policies, also counting necessarily on the unofficial part that requires changes in habits and behaviors of people who are generally influenced by complex social and psychological processes.
The Kyoto Protocol, signed in 1997 in Japan, is a commitment among the member states of the United Nations (UN) that aims to reduce greenhouse gas emissions and consequently global warming. This agreement came into force in 2004 and its targets intended to be achieved from 2008 to 2012.
In 2005, during the Conference of the Parties serving as the Meeting of the Parties to the Kyoto Protocol, which took place in Montreal, Canada, the Working Group to deal with further commitments for Annex I Parties of the Kyoto Protocol (regarding the periods following 2008–2012) was established.
According to Veiga (2009, p. 24), the European Union had committed to reduce its emissions by 20% by 2020, in relation to 1990, and declared to be willing to increase this target to 30%, depending on the overall arrangement of the new regime to be in force from 2012. Other European countries that are not part of the EU also engaged in this proposal; Japan, after its 2009 election, promised 25% by 2020 and Norway in October 2009 announced its disposal to reduce 40% by 2010.
During the 21st Conference of the Parties on Climate Change (COP21) to the United Nations Framework Convention on Climate Change (UNFCCC), in 2015, the parties signed the Paris Agreement, a treaty that aims to keep the global temperature rise far below 2°C (in relation to pre-industrial levels).
The agreement came into force on November 4, 2016, and, according to Kossoy (2018, p. 1), among the 197 countries that are part of the Conference, 180 ratified the agreement. Each country established its commitment, and the contribution Brazil promised was considered one of the most ambitious, as the country committed to implement actions that would reduce greenhouse gas emissions by 43% by 2030, in relation to the level recorded in 2005.
The life of the whole planet is threatened if humans did not become definitely aware of their responsibility to keep the balance of nature. All human development must be thought within the concepts of preservation and environmental sustainability, aiming quality of life, and more than that, ensuring life itself—the existence of life on Earth.
Recife, May 15th, 2019.
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how to quote this text
VERARDI, Cláudia Albuquerque. Global warming and greenhouse effect. In: PESQUISA Escolar. Recife: Fundação Joaquim Nabuco, 2019. Available from:https://pesquisaescolar.fundaj.gov.br/pt-br/artigo/aquecimento-global-e-efeito-estufa/. Access on: dia mês ano. (Ex.: 6 ago. 2020.)