Earth Day 2021: 10 things we’ve learned about Earth since the last Earth Day

The Bay Bridge across San Francisco Bay at twilight, with the sky orange with smoke.On September 9, 2020, smoke from wildfires burning across California blew over San Francisco, turning the sky blood orange. Gabrielle Lurie/The San Francisco Chronicle via Getty Images

10 things we learned about Earth since the last Earth Day


The secret to wombat poop, how skies turn orange, and what a cold ocean blob could mean for the climate.


This story is part of Down to Earth, a new Vox reporting initiative on the science, politics, and economics of the biodiversity crisis.

This time last April, on the 50th anniversary of Earth Day, the world was coming to grips with the isolation of quarantine and the economic and travel slowdowns that defined the first wave of the Covid-19 pandemic. Even now, with the rollout of vaccines, the virus continues to affect our daily lives. And the toll keeps growing: 3 million dead and more than 140 million cases worldwide.

If anything, the worst public health crisis in a century has brought our understanding of our planet, and our place in the fragile yet resilient web of life throughout it, into stark relief.

Amid so much grief and loss and uncertainty, the biodiversity crisis paced ahead over the past year, becoming a much bigger theme on the world stage. The climate crisis worsened, too. Wildfires blazed. Ecosystems became even more fouled up than they already were. A tree-heavy Google Doodle marking the occasion of Earth Day this year drives it all home.

At the same time, the marked reduction in human activity spurred by the pandemic — what some experts have dubbed the “Anthropause” — has afforded scientists and researchers opportunities to observe the natural world like never before. Coinciding with these unique observational windows has been an increase in attention on Indigenous knowledge and land stewardship as a way forward in combating ecological catastrophe.

1) We saw just how quickly ocean noise pollution can drop, and how much that can help marine life

For a moment last spring, things got very quiet in the oceans.

The drop in human activity that came with the pandemic resulted in drastic and voluntary sound reductions that ran the underwater gamut: from a drop in shipping noise, the predominant source of man-made ocean noise pollution, to decreases in recreation and tourism. All of it suddenly ceased.

In Alaska’s Glacier Bay National Park, the foraging grounds of humpback whales, the loudest underwater sounds last May were less than half as loud as those in May 2018, according to a Cornell University analysis. A May 2020 paper in the Journal of the Acoustical Society of America found that underwater noise off the Vancouver coast was half as loud in April as the loudest sounds recorded in the months preceding the shipping traffic slowdown.

Chronic underwater ocean noise had been rising over the past few decades, to the detriment of marine life that have evolved to use sound to navigate their world. “There is clear evidence that noise compromises hearing ability and induces physiological and behavioral changes in marine animals,” reads an assessment of marine noise pollution research published in the journal Science in February.


A humpback whale.A humpback whale seen near Shetland Islands, Scotland, December 2016. Richard Shucksmith/Barcroft Im/Barcroft Media via Getty Images


The majority of ocean noise pollution is a byproduct of economic activity. But compared with massively complex issues like climate change, noise is relatively easy to turn down, at least a little. Silencing it at its source has an immediate positive impact: Famously, researchers studying right whales on the East Coast measured a drop in the animals’ stress hormones in the wake of the 9/11 attacks, after shipping traffic abruptly dropped. Even tiny fish larvae are better able to locate the coral reefs where they were born, which themselves emit sound, when the oceans get quiet.

Man-made ocean noise has since ramped back up and is now stabilized near pre-pandemic levels. But it fell silent for long enough last March, April, and May that a global team of scientists is actively scrubbing through audio recordings gathered by around 230 non-military hydrophones — underwater microphones — that monitor ocean noise around the world. They aim to study the “year of the quiet ocean” in the context of ocean sounds before, during, and after the pandemic.

2) A new study found that the Amazon is likely warming — not cooling — the planet

The world’s largest and most species-rich tropical forest, the Amazon, is home to billions of trees that not only provide refuge to a diverse assemblage of organisms but also store and absorb a huge amount of carbon dioxide.

That’s what makes the conclusion of a study published this spring so alarming: Due to human activity, the Amazon is likely contributing to — not offsetting, as one might expect— global warming. “The current net biogeochemical effect of the Amazon Basin is most likely to warm the atmosphere,” the researchers wrote in the paper.


A deforested region of the Amazon in the municipality of Melgaco, Para State, Brazil on July 30, 2020. Tarso Sarraf/AFP via Getty Images


While the Amazon is still absorbing loads of CO2, human activities in the basin, such as deforestation, are driving up emissions of CO2 and other more potent greenhouse gases like methane and nitrous oxide across the basin.

Deforestation, for one, deals a double punch: It both releases gases into the atmosphere and removes CO2-absorbing trees from the equation. That equation now sees the Amazon generating more greenhouse gases than it emits, the study suggests. (It’s worth noting, though, this is all really complicated. For more, check out Craig Welch’s story in National Geographic or read the full study here.)

3) We discovered a bunch of new species

While humans have made a mark on all corners of Earth, we’ve only discovered a small fraction of the species that occupy it. In fact, that fraction could be smaller than 1 percent. And remarkably, not all of those species are tiny microbes and insects. They’re also fish, lizards, bats, and even whales. That’s right: Even giant mammals can elude scientists.

In January, researchers at the National Oceanic and Atmospheric Administration said they discovered a new species of baleen whale in the Gulf of Mexico. (You can find the paper describing the discovery here.) Other teams of scientists are also on the trail of what could be yet another new whale species.


A thumbnail-sized chameleon resting on top of a finger.Brookesia nana, a recently discovered species of chameleon native to northern Madagascar. AP/Frank Glaw


Last year, researchers documented scores of new plants and animals, from geckos and sea slugs to flowering plants and sand dollars, as Vox’s Brian Resnick reported. Our favorite? Brookesia nana, a thumbnail-sized chameleon native to northern Madagascar. It may be the smallest reptile on Earth; it’s certainly the cutest.

4) We got a much clearer picture of just how much wildlife we’re losing

The numbers aren’t good.

In September, the World Wildlife Fund published a report showing that the global populations of several major animal groups, including mammals and birds, have declined by almost 70 percent in the last 50 years due to human activity.

A separate report, published in Nature this year, found that populations of ocean sharks and rays have plummeted by more than 70 percent in roughly the same period. And one-third of freshwater fish have been found to be at risk of extinction.


Two gray reef sharks swim over a coral reef.Two gray reef sharks swim over a coral reef in Gambier Archipelago, French Polynesia, on February 19, 2018. Alexis Rosenfeld/Getty Images


A number of species were also declared extinct over the last year. Those include the smooth handfish, a bottom-dweller that rests atop human-like appendages on the seafloor. It was the first marine fish species to be declared extinct in modern history. (Environmental journalist John Platt has a list of recent extinctions in 2020 at Scientific American.)

5) Protecting plants and animals hinges on a thriving ecotourism industry

In the early days of the pandemic, the popular “Nature is healing” meme overshadowed a darker reality in many parts of the world: As travel ground to a halt, so did revenue from wildlife tourism, putting some wildlife conservation efforts at risk.

The fallout was most severe in Africa. According to a new collection of research from the International Union for Conservation of Nature (IUCN), a government and civil society group, more than half of the continent’s protected areas had to pause or limit field patrols and other operations to stop poachers in the wake of the pandemic.

“Parks have emptied out to a large extent and there’s no money coming in,” Nigel Dudley, a co-author of one of the IUCN papers, told Reuters last month

A mountain gorilla surrounded by trees.A mountain gorilla in Bwindi Impenetrable Forest in Uganda. Roger de la Harpe/Universal Images Group via Getty Images


Some communities are deeply reliant on wildlife tourism. Late last year, Vox’s Brian Resnick spoke to veterinarian Gladys Kalema-Zikusoka, who is working to keep coronavirus-susceptible gorillas alive in Uganda’s Bwindi Impenetrable National Park.

When tourism dropped, “everybody was struggling,” she said. “The local economy suffered and poaching went up.” (You can read more of Resnick’s conversation with her here.)

6) Researchers uncovered more proof that a key system of ocean currents is weakening

Graphics that show changes in ocean temperature over time generally reveal one trend: The ocean is heating up. But there’s one critical exception. Just below Greenland lies a large patch of water that’s cooling off. And that patch has scientists concerned that we could be nearing a tipping point for the climate.

The cold patch, scientists say, signals that a network of currents that bring warm water to the North Atlantic — known as the Atlantic Meridional Overturning Circulation, or AMOC — is slowing down, and the melting of ice on Greenland is likely a culprit. One paper, published in the journal Nature in March, suggests that the current AMOC slowdown is “unprecedented in over a thousand years.”


NASA GoddardOcean surface currents between June 2005 and December 2007. NASA Goddard


The AMOC shapes weather across multiple continents, so any major slowdown will carry major consequences that could include faster sea-level rise in some regions, stronger hurricanes, and other changes in weather, to say nothing of the impacts to marine ecosystems.

But to be clear, the science on this is new and complex. For a great run-down, check out this recent visual feature in the New York Times.

7) The asteroid that killed the dinosaurs gave rise to the Amazon rainforest

The massive asteroid that struck Earth 66 million years ago may be best known for driving non-avian dinosaurs to extinction, but it also transformed entire ecosystems.

It may have even given rise to the Amazon rainforest, according to a study published in Science earlier this month. The finding is based on an analysis of about 50,000 fossil pollen records and 6,000 fossil leaf records in Colombia from before and after the asteroid crashed into what is now Mexico’s Yucatan Peninsula.

The data reveals two vastly different forests. Before the event, the forests were stocked with conifers and ferns, and the trees were spread out, with plenty of room for light to stream through the canopy. After the asteroid event, however, flowering plants started to dominate the landscape and the canopy became much more tightly packed, resembling the forest we know today.


A part of the Amazon rainforest in Brazil.The Amazon rainforest in Belém, Brazil. Getty Images


“If you returned to the day before the meteorite fall, the forest would have an open canopy with a lot of ferns, many conifers, and dinosaurs,” study co-author Carlos Jaramillo of the Smithsonian Tropical Research Institute in Panama told New Scientist. “The forest we have today is the product of one event 66 million years ago.”

The idea here is that the asteroid impact somehow triggered a series of events that led to the modern Amazon rainforest. What were those events? One theory the researchers offer is that, before the asteroid, herbivorous dinosaurs prevented the forest from becoming dense by eating and trampling plants.

8) A review of more than 300 studies showed that the rate of deforestation is lower on Indigenous lands

The global conservation movement is pushing forward a plan to conserve 30 percent of the Earth by 2030 — an initiative known as 30 by 30 — and increasingly calling for Indigenous communities to be central to that effort.These groups have historically been uprooted from land in the name of wildlife conservation. There is also greater evidence that forests fare better when they are governed by Indigenous and tribal territories.


Women combing through leaves of the xate plant.In Guatemala’s Maya Biosphere Reserve, members of the local community harvest and sell palm fronds of the xate plant, which are used in flower arrangements. Johan Ordonez/AFP via Getty Images


A recent UN review of more than 300 studies found that forests within tribal territories in Latin America and the Caribbean have significantly lower rates of deforestation where land rights are formally recognized.

“In just about every country in the region Indigenous and tribal territories have lower deforestation rates than other forest areas,” wrote the authors of the report, which was published by the UN’s Food and Agriculture Organization and the Fund for the Development of Indigenous Peoples of Latin America and the Caribbean. “Many Indigenous territories prevent deforestation as effectively as non-Indigenous protected areas, and some even more effectively.”

9) Wildfire smoke can turn the sky an apocalyptic orange

If there was one day in 2020 that defined the climate emergency, it could have been September 9, when the sky above San Francisco turned completely orange.

Smoke from wildfires turned the sky above San Francisco orange on September 9, 2020. Jessica Christian/The San Francisco Chronicle via Getty Images


Strong winds had carried smoke from fires burning across California to the atmosphere above the city. Particles of soot absorbed or reflected blue light from the sun, letting only orange-ish light through. (Wired has the details.)

But what made the image go viral wasn’t so much the science but what it symbolized: a growing climate catastrophe.

Climate change is making wildfires more frequent and severe, and 2020 provided more devastating evidence. Last year was California’s worst wildfire season on record. By the end of the year, nearly 10,000 fires had burned over 4 million acres — an astonishing 4 percent of California’s total land, according to the state.

10) Scientists finally solved the mystery of why wombats poop cubes

Sure, it may not have kept you up at night, but the mystery of the bare-nosed wombat’s poop puzzled scientists for decades. Why do these adorable, chunky marsupials, native to Australia and Tasmania, leave behind feces with six sides?

Thanks to a new study — published in the journal Soft Matter — we now have the answer.

Cube-shaped poop from wombats in Australia.Cube-shaped wombat poop in Kosciuszko National Park in Australia. Getty Images


Building on research published a few years earlier, a team of scientists found that wombat intestines have regions of varying thickness and elasticity that contract at different speeds: The stiffer regions contract relatively quickly, while softer sections squeeze more slowly, together forming a cube-like shape.

But there’s still a bit of mystery left: Why is their poop shaped like this? The jury’s still out, but some researchers believe it’s because wombats climb up on rocks and logs, and the cube-like shape prevents the feces from rolling away. This is key for wombats because they use piles of feces to communicate with other wombats.

What a difference a year makes, truly.

By Benji Jones and Brian Anderson|April 22, 2021