The tropics, a region around the Earth’s equator, are experiencing changes influenced by natural processes and human activities. This expansive zone, known for its warm, wet conditions, is a hub of biodiversity and home to a significant portion of the global population. Understanding the state of the tropics involves examining its geographic characteristics, evolving climate patterns, the health of its diverse ecosystems, and the interactions of its human inhabitants.
Defining the Tropical Zone Today
The tropical zone is defined by the Tropic of Cancer in the Northern Hemisphere (approximately 23.5°N) and the Tropic of Capricorn in the Southern Hemisphere (approximately 23.5°S). These latitudes mark where the sun can be directly overhead at least once annually. This region experiences consistent warmth, with mean annual temperatures often exceeding 20°C.
The tropics lack distinct temperature-based seasons, instead exhibiting variations primarily in precipitation, leading to wet and dry periods. While the equatorial zone maintains consistent warmth and minimal day-to-day temperature fluctuations, the edges of the tropics can be drier and hotter. The Earth’s axial tilt, around 23.4°, dictates the boundaries of these tropical circles.
Current Climate Dynamics
The climate dynamics in the tropics are influenced by the Intertropical Convergence Zone (ITCZ), a band of low pressure near the equator where prevailing winds converge, leading to rainfall. In 2023, the ITCZ exhibited a northward shift, contributing to drier-than-average conditions across parts of the Maritime Continent, central and eastern Pacific, eastern Australia, Central America, and northern South America. This pattern was associated with the transition from La Niña to El Niño conditions, which strengthened throughout the latter half of 2023.
Tropical regions have experienced warming, with the average temperature in the global tropics reaching 0.5°C above the 1991–2020 average in 2023, making it the warmest year on record since 1850. The six warmest years in the tropics have all occurred since 2015. This warming trend is also contributing to the poleward expansion of the tropics, driven primarily by ocean warming linked to human-caused climate change.
Ecological Health and Biodiversity
Tropical ecosystems are renowned for their biodiversity, encompassing dense rainforests, expansive savannas, coastal mangroves, and vibrant coral reefs, which together host nearly two-thirds of all known species. The health of these ecosystems is under stress from human activities. Deforestation and habitat degradation represent pressures, directly impacting the species in these biomes.
Climate change is also a driver of ecological decline in the tropics, influencing specific species and altering ecosystem functions. The loss of biodiversity in these regions is occurring at an accelerated rate, with current species extinction rates estimated to be 10 to 100 times higher than natural baseline levels. Conservation efforts are ongoing, involving research and initiatives to identify stressors and inform policymakers.
Human Presence and Development
Tropical regions are home to a substantial human population, with approximately 40% of the world’s inhabitants residing there, projected to reach 50% by 2050. These communities engage in diverse socio-economic activities that shape the landscape, including agriculture, tourism, and resource extraction. For example, artisanal and small-scale gold mining is a source of mercury emissions, impacting both the environment and human health.
Demographic trends in tropical areas reflect a complex interplay of development and environmental adaptation. While progress has been made in reducing extreme hunger in some parts of Latin America and the Caribbean, other regions like sub-Saharan Africa continue to face challenges, with undernourishment increasing in almost all areas. Communities are also adapting to environmental changes, including more frequent extreme weather events and higher wet-bulb temperatures, which could push parts of the tropics to the limits of human livability.