Climate change, caused by greenhouse gas concentration, has significantly impacted the Earth in the last three decades. Global terrestrial and sea temperatures are rising, sea levels are rising, land ice coverage is reduced, and there are more extreme weather events like heat waves or cyclones. In the 1930s, Callendar presented evidence of increased greenhouse gas concentration due to human activities leading to higher temperatures. The Intergovernmental Panel on Climate Change (IPCC) reported a temperature increase of about 1.1°C between 1850 and 2020, with the primary increase occurring from 1970 onwards.
This blog post will investigate the impacts of climate change in tropical forests, including rainfall, temperature, and extreme climatic events, to examine their effects on vertebrates living in these forests. The study focuses on Central America, the Amazon basin, West and Central Africa, Madagascar, Southeast Asia, and Northeast Australia.
Climate Change in Tropical Forests
The tropics and subtropics are anticipated to experience more severe warming than the mid-latitudes. For most tropical regions, the climate is relatively stable, with constant temperatures throughout the year. They, however, experience an interannual climatic variable caused by El Niño and La Niña. Which respectively represent a warming phase and a cooling phase. These events are not entirely understood, but they cause variations in temperature and precipitation in South American and Southeast Asian tropical regions. Since 1976, the intensity and frequency of El Niño events have increased relative to La Niña events. Due to large and non-linear responses, it is challenging to simulate these events in climate models. Leading to more uncertainty in the projections of climate change in tropical regions.
Since the mid-1970s, the tropical regions have experienced a temperature increase ranging from 0.15°C to 0.40°C per decade. If global temperatures increase by 2°C, the tropics are projected to experience a rise in temperature between 1.5°C and 2.5°C. Even though the increase is lower than in other parts of the world. Experience projections suggest that the tropical regions will experience extreme conditions sooner than other regions, even with an increase of 1°C or less.
Change in Rainfall
During the same timeframe, the tropical regions have experienced a decrease in precipitation of 1.0 ± 0.8% per decade. However, not all regions are experiencing a decrease in precipitation. Southeast Madagascar experienced an increase in precipitation between 2005 and 2016. At 2°C, the IPCC simulated that changes in precipitation in the Amazon region, parts of Southeast Asia, and parts of tropical Australia will become drier. While Western and Central Africa, Madagascar, and other parts of Southeast Asia and Australia will become wetter. Most areas will not only see a change in the total annual precipitation but also seasonal distribution and interannual variability. An increase in seasonal distribution and interannual variability may lead to new or prolonged drought seasons in tropical forests.
The IPCC analyzed soil moisture levels and found that precipitation levels strongly correlate with these levels, but they also vary due to evapotranspiration. They predicted that Southeast Asia and Northeast Australia would experience a small decrease in soil moisture levels. While the Amazon basin would experience a significant decrease. In West and Central Africa, higher soil moisture levels are expected to correspond to an increase in rainfall. Interestingly, the areas that will receive more rainfall in Southeast Asia and Australia do not follow this same pattern. Overall, scientists anticipate significant climate changes in tropical regions over the coming decades. It remains unclear how invertebrates inhabiting these areas will be affected.
Extreme temperatures
Tropical invertebrate species are highly sensitive to extreme temperatures caused by global warming. These species evolved in areas where there is minimal temporal temperature variation. Even a small temperature increase can have a significant fitness impact on these species. Global climate models predict not only a change in the intensity but also the duration and frequency of extreme temperatures. As a result, more species will become exposed to extreme temperatures. While species all over the world will become exposed, the biggest increases are for the species in tropical areas. Large areas will have 100% of the species being exposed to extreme temperatures.
Droughts
The frequency of droughts will increase with expected changes in climate. While droughts will mostly impact Northern America and Europe, tropical forests are also affected. It is important to distinguish between droughts and dry seasons when talking about drought in tropical forests. Tropical rainforests have a dry season naturally. Droughts in tropical forests are associated with an increase in forest fires. Increased temperatures and decreased precipitation caused by climate change can make the forest susceptible to fires. The fires start a positive feedback loop, opening the canopy, decreasing humidity, and making the forest even more susceptible to fires.
Abundance
Tropical ecosystems hold extraordinary biological diversity, with a high degree of endemism. Tropical animals often have reduced dispersal abilities and a high degree of specialization, making them vulnerable to climate change. The increased temperatures and prolonged and more frequent droughts are generally expected to result in a decline in species abundance in the tropics. These effects are already visible in different tropical regions and taxa.
Range shift
Biologists have recognized the importance of climate as a major driver of species distribution for centuries. Therefore, we expect shifts in species ranges. Species show upwards movement in elevation not only to escape heat stress but also due to reduced moisture levels caused by increasing temperatures.
Phenological changes
Climate strongly influences phenology, which response to subtle changes in day length variation, solar irradiance, insolation, moisture availability, and temperature. Climate change has frequently caused shifts in phenology. However, long-term studies are scarce, making observations of phenological shifts in tropical plants and animals rare. Phenology in the tropics is complex, as it is influenced by several abiotic factors and significant levels of intraspecific and interannual variation.
Extinction due to climate change in tropical forests
Climate change is generally expected to cause a decline in species abundance, rather than an increase. However, species can survive in changing climates through changes in elevation range. These changes also affect patterns of biodiversity and communities, resulting in reduced fitness, population declines, and increased extinction risk. The higher tropical forest areas will experience a greater relative abundance of warm-adapted and low-elevation species. Which leads to increased competition between the lowland species moving upwards and the endemic mountain species. This results in reduced fitness, population declines, and increased extinction risk for both. Climate change is expected to generate a greater community dismantling in tropical regions due to the high species turnover, compared to temperate regions. Lastly, the change in phenology brings another increased risk of extinction as asynchronous shifts in phenology could lead to trophic mismatches between interacting species, causing cascading effects on tropical communities.
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