International Day of the Tropics

Here is a single statistic to sit with: the tropics cover roughly 40 per cent of the Earth’s surface yet hold about 80 per cent of its living species. That belt around the planet’s middle, warm year-round and drenched in sunlight, is where life has piled up most thickly, in rainforests, reefs, mangroves and savannahs. It is also where humanity is concentrating fastest, on track to hold a majority of the world’s people within a few decades. The International Day of the Tropics, observed each 29 June, asks the rest of the world to pay this region the attention its weight deserves, both for what it shelters and for the pressures bearing down on it.

Where the day comes from

The starting point was a document, not a ceremony. On 29 June 2014, twelve leading tropical research institutions jointly published the inaugural State of the Tropics report, an attempt to treat the tropical world as a single subject and to assemble hard data on its environment, economy and society. The report’s central insight was that the tropics, too often studied piecemeal country by country, share challenges and trends that only become visible when viewed as a whole.

The report gave the day its date. Two years later, in 2016, the United Nations General Assembly adopted resolution A/RES/70/267, declaring 29 June, the anniversary of the report’s launch, the International Day of the Tropics. The stated aim was to raise awareness of the specific challenges tropical regions face and to underline the part tropical nations will play in meeting the Sustainable Development Goals.

What and where the tropics are

Geographically the definition is precise. The tropics are the band lying between the Tropic of Cancer at about 23.5 degrees north and the Tropic of Capricorn at the same latitude south, with the Equator running down the middle. Within this band the Sun passes directly overhead at least once a year, which is exactly what the boundary lines mark. The result is warmth through every month and, in much of the region, a rhythm of wet and dry seasons rather than the spring-to-winter cycle of temperate zones.

The lands inside this belt are anything but uniform. They take in the rainforests of the Amazon and the Congo, the savannahs of East Africa, the mangrove coasts of South-East Asia, the coral archipelagos of the Pacific and arid stretches besides. They span Central and South America, sub-Saharan Africa, southern Asia and the island nations of the Pacific and Caribbean.

Why it matters

The case for caring about the tropics begins with biodiversity. Naturalists have long puzzled over why life crowds towards the Equator and thins towards the poles, a pattern so consistent it has a name, the latitudinal diversity gradient. Whatever its ultimate cause, the consequence is that the tropics hold the lion’s share of the planet’s species, many still undescribed by science, in forests and on reefs that rank among the richest ecosystems anywhere.

These systems do work that reaches far beyond the region. Tropical forests store immense quantities of carbon and help drive global rainfall patterns; the reefs that fringe tropical coasts, which the world pauses to consider on World Oceans Day, shelter a quarter of all marine species and protect coastlines from storms. The human stakes are rising in step. A large and growing share of humanity lives in the tropics, many of its nations are developing rapidly, and yet the region carries an outsized burden of deforestation, biodiversity loss, water stress and the sharp end of climate change.

How it is observed

As an awareness day rather than a holiday, 29 June is marked chiefly through the spread of knowledge. Universities, research bodies, environmental organisations and UN agencies use the occasion to release findings, host seminars and convene discussions on conservation and sustainable development. Online events and conferences explore themes that shift from year to year but circle the same concerns: how to develop without destroying, and how to share the burden of protecting systems that benefit everyone.

Schools and community groups often take the day as a prompt to teach about tropical ecosystems and the species they hold. A recurring thread is the link between distant decisions and tropical consequences, the way a shopping basket in a temperate city can reach back through supply chains to a forest near the Equator. Coffee, cocoa, palm oil, rubber and bananas all grow in the tropics and are consumed largely outside them, which means the comfortable habits of richer, cooler countries are quietly written into the fate of tropical land.

A region under pressure

The vulnerabilities the day exists to flag are not evenly spread, and naming them concretely matters more than gesturing at “challenges”. Deforestation remains the starkest: the Amazon, the Congo basin and the forests of South-East Asia are being cleared for cattle, soy, palm oil and timber at a pace that threatens both their biodiversity and their role as carbon stores. The same warmth that makes the tropics so fertile also makes them a crucible for disease, with malaria, dengue and other illnesses concentrated in the band and likely to spread as the climate warms.

Then there is the paradox of water. The tropics hold just over half the world’s renewable freshwater, yet nearly half their population is reckoned vulnerable to water stress, a mismatch driven by uneven distribution, rapid urban growth and the increasingly erratic rains that climate change brings. Add rising seas threatening low-lying island nations and coastal cities, and the region emerges as a place where the consequences of global decisions arrive first and hit hardest, often in the countries least responsible for causing them.

The human tropics

The region’s diversity is cultural as well as biological. The tropics are home to a vast array of peoples, languages and traditions, including many Indigenous communities whose detailed knowledge of local ecosystems has been refined over countless generations. The day frequently foregrounds this human dimension, on the understanding that the fate of tropical forests and reefs is inseparable from the livelihoods of those who live among them. Conservation that ignores the people of a place rarely holds.

Because the tropics sprawl across so many countries, observances differ markedly. A Caribbean island may focus on reefs and rising seas, an Amazonian state on deforestation, a Pacific nation on freshwater and food security. The variety of the events mirrors the variety of the region itself.

There is also a question of voice running beneath the day. For a long time the tropics were studied and described chiefly by outsiders, from temperate-latitude scientists and colonial administrators, whose accounts often cast the region as either an exotic paradise or a hazardous frontier. A growing share of tropical research is now led by institutions within the tropics themselves, and the day increasingly platforms experts and communities from the region rather than treating them as subjects to be observed. Who gets to speak for the tropics turns out to matter almost as much as what is said.

Symbols of the day

The imagery is drawn straight from tropical abundance: the towering green of a rainforest canopy, brilliantly coloured birds and flowers, coral gardens beneath clear water, and the warm, saturated light of the equatorial world. Even the rainbows of the region carry meaning here, for the heavy convectional downpours that feed tropical forests are precisely the conditions that throw arcs of colour across the sky, the kind celebrated on Find a Rainbow Day. These symbols do double duty, standing for both the richness of tropical life and the urgency of its protection.

Fun facts

• The word “tropic” comes from the ancient Greek tropos, meaning a turn, because the Tropics of Cancer and Capricorn mark the latitudes where the Sun appears to turn back on its seasonal journey.
• The tropics hold just over half of the world’s renewable freshwater, around 54 per cent, yet nearly half of their population is considered vulnerable to water stress, a striking mismatch between supply and security.
• The Tropic of Cancer is slowly drifting south and the Tropic of Capricorn north, each shifting by roughly fifteen metres a year because of small wobbles in the tilt of the Earth’s axis.
• The first State of the Tropics report, which gave the day its date, was the work of twelve research institutions collaborating across continents rather than any single country or agency.

A closing reflection

It is tempting for those who live in temperate latitudes to think of the tropics as somewhere else, a destination or a documentary backdrop. The day quietly dismantles that distance. The carbon stored in an Amazonian tree, the rain pattern shaped by a distant forest, the species that may yet yield a medicine, all of these tie the comfortable middle latitudes to the crowded, sweltering, extravagantly alive band around the Equator. To mark 29 June is to admit that the line between “here” and “the tropics” was always a fiction of maps, and that the planet keeps most of its riches in a place a great many of us have learned to overlook.