Past and Future Climate Change: Understanding Earth’s Climate
Past Climate Change
A) Variations in the Earth’s Climate Before the Quaternary
We know that from the early history of Earth, land and sea distribution was different, undoubtedly impacting the Earth’s climate. We know of the existence of a large continent called Pangaea. This continent would have acted as a brake on ocean currents, preventing them from reaching the middle and high latitudes, which would have remained very cold, resulting in an ice age affecting the highest mountain summits. This would explain both the Precambrian glaciation and Carboniferous glaciation since they correspond respectively to Pangaea I and II.
However, during the elapsed time between the two, there was the fragmentation of Pangaea I, which led to intense circulation of ocean currents. As a result, the average temperatures during the Paleozoic were higher than those at present. Moreover, we know that continents have a higher thermal amplitude, so in winter, the cold air is very intense, mashing against the ground and causing a permanent anticyclone. In anticyclones, the wind is cold and dry, flowing from the inside towards the edges, resulting in an arid and desert climate. That was what happened during the Permian desert, influenced by the large anticyclone formed on the supercontinent Pangaea II.
During the Mesozoic and Tertiary, the temperature rose even more, especially in the Cretaceous and Jurassic, when Pangaea II divided into two continents. The climate became very favorable for the development of large tropical reptiles. In the late Mesozoic, the extinction of dinosaurs took place, which was apparently due to the impact of a meteorite.
B) Variations in Temperature During the Quaternary
Since the beginning of the Quaternary to the present, the distribution of land and seas has hardly changed. Therefore, explanations for climate variations have resorted to variations in incident solar radiation caused by Milankovitch cycles. Over the past 800,000 years, the Earth has gone through glacial periods lasting about 100,000 years, separated by interglacial periods of about 10,000 years. The existence of these glaciers has been studied from the analysis of air bubbles trapped within the ice of glaciers. It has been shown that during periods of cooling, the air contained a lower proportion of CO2.
C) Changes in Temperature During the Historical Past
Approximately 10,000 years ago, the last Quaternary glaciation ended, and the warm interglacial period began. The Holocene warming, called the Holocene Climatic Optimum, occurred during this period, with temperatures 2 or 3 degrees higher than our current climate. After this time, there was an alternation of warm and cold periods, mainly leaning towards the latter from 100-1200 AD, when the Medieval Warm Period (MWP) enabled Viking exploration of the North Atlantic. Then there was a more marked cooling period, the Little Ice Age (between 1200-1900 AD), when a kind of small ice age occurred, marked by the advance of polar ice.
Sunspots: They are dark areas that appear on the sun’s surface and increase in number, reaching a maximum approximately every 11 years. The intensity of solar radiation falling on Earth is 1370W/m2 on average, and the maximum sunspot activity can increase this by 1.2 W/m2. However, the total number of sunspots varies in cycles of 80 and 180 years, during which a decrease or increase in the maximum number of spots occurs. These intervals may be the cause of all the thermal variations that occur during a decrease in the maximum number of sunspots, as in the case of the Little Ice Age. During this period, the Arctic froze, extending the polar anticyclone, which is also a place of negative North Atlantic Oscillation (NAO) and a weak Westerlies wind pattern, which originates winter rains in our country.
Climate Change and the Future
The current global warming is a major problem because it is global. The Convention on Climate Change conference in Rio de Janeiro in 1992 noted that human activities, particularly greenhouse gas emissions, have increased the average temperature of the Earth. It was concluded that if developing countries follow our model of uncontrolled exploitation, greenhouse gas emissions will skyrocket.
In the past few thousand years, the atmospheric concentration of CO2 remained around 280ppm, but since the industrial revolution, it has risen to 370ppm in 2007. Indeed, CO2 is primarily responsible, but not the only culprit: methane, nitrous oxide, F-gases, hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulfur hexafluoride (SF6) also contribute. According to the fourth IPCC report published in 2007, the forecasts are:
- Melting ice will decrease the albedo, so temperatures will rise further.
- There will be a dangerous increase in icebergs.
- Climate zones will shift toward the poles at a rate of about 5 km/year, causing changes in subtropical ecosystems and the advance of deserts.
- Alterations in the water cycle and a reduction in its quality will occur.
- Health problems due to hunger and disease resulting from a reduction in crops will arise.
International Agreements
In the 3rd Conference of the Parties (COP) of 1997, the Kyoto Protocol was signed, representing a first step to curb greenhouse gas emissions. At the summits held in the following years, three flexibility mechanisms were outlined:
- Emissions Trading: A country may buy another country’s emission rights, allowing them to reach their goals.
- Clean Development Mechanism (CDM): Developed countries can promote and invest in clean development projects in developing countries.
- Inclusion of Carbon Sinks: This involves partially offsetting emissions by planting trees and other plants that absorb CO2.
At the Nairobi Summit of 2006 and the Bali Summit of 2007, further discussions took place. According to a report by the Environment Agency in 2008, the EU intends to not only fulfill its commitment to reduce greenhouse gas emissions by 8% compared to the scheduled basis but also surpass it and increase it up to 11%. This figure could be achieved by including carbon sinks and credits. As we can see, the emission data in Spain are among the worst; however, it is projected to be most affected by the consequences of climate change. To avoid this, it requires a political will that prioritizes investment in renewable energy.