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The Human Impact on the World’s Forests

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World Forest Cover Map

Source: Global forest Watch

Snapshot of the World’s Forests

View the high resolution version of today’s graphic by clicking here.

Forests cover over 30% of the world’s land, but human activity is chipping away at the tree line.

At the outset of the 20th century, there was approximately 31 million square miles (50 million square km) of forest around the world. Today, that number has shrunk to less than 25 million square miles (40 million square km). Much of this decline can be attributed to expanding agricultural land use and increasing demand for wood and paper products.

Forest Gain and Loss Animation

Source: World Bank

The growth and decline of forest cover is hardly uniform. Deserts, farmland, and urban areas ebb and flow around the world, and while some countries are rapidly removing trees from their ecosystem, others are seeing increases in their forest cover.

Receding Leaf Line

Since 1990, global forested area has shrunk by 2 million square miles (3.1 million square km), with many of those losses occurring in South America and Sub-Saharan Africa.

Gained Forest Area Chart

The Amazon Rainforest, one of the most important carbon sinks on the planet, has faced intense pressure from human activity over the last few decades. Brazil’s expanding network of roads has been critical for economic development, but the landscape often pays the price as the country increases its GDP per capita.

Amazon Deforestation
Rainforest turns to farmland in Brazil’s Rondônia state: 1984–2016

Across the Atlantic Ocean, Africa is grappling with deforestation.

West Africa, for example, has lost a shocking 90% of its forest cover over the last century – in a number of countries, all of the forest outside of protected areas has been logged, while illegal logging threatens parks and reserves.

If nothing is done, we may lose everything.

– Abraham Baffoe, Africa regional director at Proforest

Forest Renewal

Images of slash-and-burn land clearing and denuded hillsides grab the headlines, however, there are a few places in the world where forests are expanding.

Europe, in particular, has seen widespread regeneration of forests over the past century.

Reforestation in Europe

Source: Wageningen

China is another, perhaps surprising, place where there have been big increases in forested areas.

Each year, dust storms blowing in from the expanding Gobi Desert displace as much as 800 square miles (2,000 square km) of topsoil and damage crops adjacent to the expanding desert. In response, the government created the Three-North Shelterbelt Program, which they hope will halt desertification. Thousands of miles of newly-planted vegetation will act like a wall, containing the spread of the Gobi Desert.

The Big Picture

Activities that lead to deforestation differ from region to region, but they’re always economic in nature. Palm oil, logging, raising cattle, and even charcoal production are all ways people can pull themselves out of poverty in developing countries.

The good news is that as per capita incomes in developing countries continue to rise, pressure on forests should lessen.

This theory is best visualized by Kuznets Curve, which demonstrates a link between economic development and environmental degradation.

kuznets curve countries
Click here to view the full sized version.

In regions with lax enforcement, corruption, and a large population of people living below the poverty line, deforestation could remain a problem until economic conditions improve. Thankfully, the five countries with the most forest cover – Russia, Brazil, Canada, U.S., and China – are on or are moving towards a more favorable side of the curve.

Another bright spot in this story is that governments are increasingly protecting habitat in the form of nature reserves and national parks. Since 1990, the amount of nationally protected land in the world has nearly doubled.

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Environment

The Most Polluted Cities in the U.S.

What are the most polluted cities in the U.S. according to data from the American Lung Association’s 2024 State of the Air Report?

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Teaser image for an infographic showing the most polluted cities in the U.S. according to the American Lung Association's 2024 State of the Air report.

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The following content is sponsored by National Public Utilities Council

The Most Polluted U.S. Cities in 2024

According to the World Health Organization, air pollution is responsible for 7 million deaths annually, and could cost the global economy between $18–25 trillion by 2060 in annual welfare costs, or roughly 4–6% of world GDP.

And with predictions that 7 in 10 people will make their homes in urban centers by mid-century, cities are fast becoming one of the frontlines in the global effort to clear the air.

In this visualization, we use 2024 data from the State of the Air report from the American Lung Association to show the most polluted cities in the United States.

What is Air Pollution?

Air pollution is a complex mixture of gases, particles, and liquid droplets and can have a variety of sources, including wildfires and cookstoves in rural areas, and road dust and diesel exhaust in cities. 

There are a few kinds of air pollution that are especially bad for human health, including ozone and carbon monoxide, but here we’re concerned with fine particulate matter that is smaller than 2.5 microns, or PM2.5 for short. 

The reason for the focus is because at that small size, particulate matter can penetrate the bloodstream and cause all manner of havoc, including cardiovascular disease, lung cancer, and chronic pulmonary disease. 

The American Lung Association has set an annual average guideline of 9 µg/m³ for PM2.5, however, the World Health Organization has set a much more stringent limit of 5 µg/m³.

The 21 Worst Polluted Cities in the U.S.

Here are the top 21 most polluted cities in the U.S., according to their annual average PM2.5 concentrations:

RankCity, StateAnnual average concentration, 2020-2022 (µg/m3)
1Bakersfield, CA18.8
2Visalia, CA18.4
3Fresno, CA17.5
4Eugene, OR14.7
5Bay Area, CA14.3
6Los Angeles, CA14.0
7Sacramento, CA13.8
8Medford, OR13.5
9Phoenix, AZ12.4
10Fairbanks, AK12.2
11Indianapolis, IN11.9
12Yakima, WA11.8
13Detroit, MI11.7
T14Chico, CA11.6
T14Spokane, WA11.6
15Houston, TX11.4
16El Centro, CA11.1
17Reno, NV11.0
18Pittsburgh, PA10.9
T19Kansas City, KS10.8
T19Las Vegas, NV10.8

Note: The American Lung Association uses Core Based Statistical Areas in its city and county rankings, which have been shortened here to the area’s principal city, or metro area in the case of the Bay Area, CA.

Six of the top seven cities are in California, and four in the state’s Central Valley, a 450-mile flat valley that runs parallel to the Pacific coast, and bordered by the Coast and Sierra Nevada mountain ranges. As a result, when pollution from the big population centers on the coast is carried inland by the wind—cities #5 and #6 on the list—it tends to get trapped in the valley. 

Bakersfield (#1), Visalia (#2), and Fresno (#3) are located at the drier and hotter southern end of the valley, which is worse for air quality. The top three local sources of PM2.5 emissions in 2023 were farms (20%), forest management / agricultural waste burning (20%), and road dust (14%). 

Benefit to Economy

While the health impacts are generally well understood, less well known are the economic impacts.

Low air quality negatively affects worker productivity, increases absenteeism, and adds both direct and indirect health care costs. But the flip side of that equation is that improving air quality has measurable impacts to the wider economy. The EPA published a study that calculated the economic benefits of each metric ton of particulate matter that didn’t end up in the atmosphere, broken down by sector. 

SectorBenefits per metric ton
Residential Woodstoves$429,220
Refineries$333,938
Industrial Boilers$174,229
Oil and Natural Gas Transmission$125,227
Electricity Generating Units$124,319
Oil and Natural Gas$88,838

At the same time, the EPA recently updated a cost-benefit analysis of the Clean Air Act, the main piece of federal legislation governing air quality, and found that between 1990 and 2020 it cost the economy roughly $65 billion, but also provided $2 trillion in benefits

Benefit to Business

But that’s at the macroeconomic level, so what about for individual businesses?

For one, employees like to breathe clean air and will choose to work somewhere else, given a choice. A 2022 Deloitte case study revealed that nearly 70% of highly-skilled workers said air quality was a significant factor in choosing which city to live and work in.

At the same time, air quality can impact employer-sponsored health care premiums, by reducing the overall health of the risk pool. And since insurance premiums averaged $7,590 per year in 2022 for a single employee, and rose to $21,931 for a family, that can add up fast. 

Consumers are also putting their purchase decisions through a green lens, while ESG, triple-bottom-line, and impact investing are putting the environment front and center for many investors.

And if the carrot isn’t enough for some businesses, there is the stick. The EPA recently gave vehicle engine manufacturer Cummins nearly two billion reasons to help improve air quality, in a settlement the agency is calling “the largest civil penalty in the history of the Clean Air Act and the second largest environmental penalty ever.”

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