Our planet Earth, our home, has a wide range of climates; and because of it, some parts of the planet are more sensitive to changes in temperature than others. Temperatures increase at different speeds with generally faster rates over land than oceans. The strongest warming is happening in the Arctic during cool seasons and in mid-latitude regions during warm seasons.
The Earth is currently 1.2°C warmer than it was during pre-industrial times; although there are areas that have already surpassed 1.5°C. Since 1880 the average temperature has increased nearly a whole degree; however, most of the increase happened after 1975. During the 21st century, every year has been on the top 20 warmest years on record. The last time the Earth was this warm was over 11,000 years ago.
In 2016, the United Nations signed the Paris Agreement. This agreement signed by 197 countries that year and ratified by 185 in 2019 brings all these nations together to undertake efforts to combat climate change. The central objective is to “strengthen the global response to the threat of climate change by keeping a global temperature rise this century well below 2 degrees Celsius above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.5 degrees Celsius”. This means that the treaty’s main goal is to keep the Earth at the average temperature that existed before factories started releasing greenhouse gases into the air.
But why 2°C? The number started circulating in the science community in 1975 thanks to Dr. William Nordhaus, an economist who saw the warming trend as a threat to the global economy. Since he knew anthropogenic CO2 was causing temperatures to rise, he calculated what would happen if the CO2 concentration in the atmosphere was doubled which equated to a global temperature increase of 2°C. He also predicted that CO2 levels would double by 2030.
The consequences of a 2°C increase above pre-industrial levels vary by location. A few of these include extreme temperatures, droughts, water availability, extreme precipitation, impacts on biodiversity and ecosystems, rise of sea level, impacts on polar ice sheets, changes in ocean’s temperatures, changes in ocean’s acidity, changes in ocean’s oxygen levels, human’s heat related illness and mortality, impact on food security, economic impacts, among others.
Extreme temperatures. Most land areas will see more hot days, especially in the tropics. If temperature rises 2°C above pre-industrial levels, 37% of the population will be exposed to severe heatwaves at least once every 5 years. The hottest temperatures will be felt in Central and Eastern North America, Central and South Europe, the Mediterranean, Western and Central Asia, and Southern Africa. In high altitudes, the coldest nights will be 6°C warmer and up to 8°C in the Arctic.
Droughts and extreme precipitation. Severe droughts and risks related to water availability will particularly affect the regions in the Mediterranean, Southern Africa, South America and Australia. People in river basins will be particularly vulnerable to climate change-induced water scarcity with an increased risk in groundwater depletion if temperatures get higher. On the opposite, some areas will see an increase of heavy rainfalls, especially in the Northern hemisphere’s high altitudes and mountainous regions like the Tibetan plateau, Southeast Asia, and Eastern North America, with higher flooding risks and an increased in runoff.
Rise of sea level. It is caused by the melting of ice sheets and glaciers and the expansion of seawater as it warms. In 2014, sea level was 2.6 inches above the 1993 average, the highest on record; and it continues to rise at a rate of one-eighth of an inch per year. Last year alone three islands disappeared, Tebunginako in Kiribati, a Hawaiian island, and a small Arctic island. If temperatures reach the 2°C increase, coastlines will see a sea level rise greater than 0.66 feet (0.2 meters) resulting in flooding, beach erosion and salinization of water supplies. Sea level rise will affect areas all around the world on different scales with South and Southeast Asia being the regions with the highest risk.
Impacts on biodiversity and ecosystems. Increases in ocean temperature are associated to increases in ocean acidity and decreases in oxygen levels which pose a significant risk to marine biodiversity and ecosystems. Increased acidity is a result of higher concentrations of CO2 which negatively impact algae production and other species. Fisheries will be affected with many marine species migrating toward higher altitudes. Ecosystems such as coral reefs will be highly threatened by ocean acidification and warming, becoming almost non-existent at the 2°C increase scenario. Loss of sea ice will impact the habitat of many species from phytoplankton to polar bears.
Energy. Hydropower generates about 24% of the world’s electricity; but less snow to melt and shifting rainfall patterns may affect the use if this energy source.
Food. Yields for crops like maize, rice and wheat among other cereals will decrease with a 2°C increase in temperature, particularly in sub-Saharan Africa, Southeast Asia and Central and South America. Food availability in general – including livestock- is also projected to decrease.
Human health. Impact will vary by region depending on the population’s ability to adapt to the new environment. Cities will experience the worst impacts of heatwaves. Disadvantaged and vulnerable populations and some indigenous communities with livelihoods based on agriculture or coastal resources will be at greater risk. More people will die from vector-borne diseases like malaria and heat-related illness. Some populations will see an increase in poverty. Furthermore, parts of the planet will become inhabitable because of extreme temperatures.
The above are only some of the impacts that a 2°C rise in temperature would cause and the threats are just around the corner. CarbonBrief has a nice graphic showing a comparison between an increase in 1.5°C vs 2°C.
NASA, Popular Science – What happens if Earth gets 2°C warmer? Video, Live Science
Featured image: Rollingstone.com