Hot Numbers
It's a fact: Human impacts are warming our climate and changing our planet
The numbers are undeniable: Our planet is warming. Humans are responsible. The impacts are profound. But together we can fix it.
Scientists agree that human impacts, including climate change, habitat destruction, and resource consumption, are threatening the health of the natural systems upon which we all depend for our long-term well-being.
Climate and sustainability issues are complex, and their impacts are far-reaching. They're also difficult to grasp and even more challenging to summarize. Distilling complex issues into a few numbers risks oversimplification, but doing so can help us get our heads around some big concepts.
Facts may never convince the deeply skeptical. For the rest of us, facts do matter. They can be an important reminder. They can startle us out of complacency. They can move us to action.
With that in mind, we've compiled a list of twelve numbers that provide a concise overview of the challenges we face. Use them as a personal motivator. Slip them into conversations with your friends—but try to separate science from politics, facts from emotion.
Knowing that scientific facts alone aren't enough, we conclude this story with some things that all of us can do to respond to these vitally important issues.
C A U S E S
Earth's human population will reach 9 billion by 2050.
The number of humans living on the planet didn't reach one billion until the year 1804. Then, in just 113 years, the world's population doubled, reaching two billion in 1927. Today, our numbers exceed 7.2 billion.
2050 population projections actually range from 9.4 billion to 10.1 billion. Educating and empowering women, and providing them with access to reproductive healthcare, typically reduces fertility and can help lower future population growth rates.
Sources: UNESCO and Project Drawdown
Only 25 percent of Earth’s land surface is relatively free of human impacts.
The human footprint extends to the far corners of the planet. Roads reach into wildernesses; forests fall to logging, rangeland, and agriculture.
Source: WWF Living Planet Report
The Wildlife Conservation Society's "human footprint" map, shown above, combines land cover information with transportation networks to reveal the sprawling impact of human activities. Our global reach and ability to alter vast landscapes necessitate careful stewardship of the finite natural heritage on which we all depend.
Source: WCS | Explore live map
Humanity demands nearly twice as much from the planet than what its ecosystems renew. It is like using the equivalent of 1.7 Earths.
People compete for the productive areas of the world to produce food, fibers and timber, to accommodate houses and roads, and to absorb waste, particularly carbon dioxide from fossil fuel burning. As this use exceeds what Earth can renew, we are depleting our planet, including changing the composition of the atmosphere, draining ice-age groundwater, overfishing oceans, logging ancient forests, and losing rich soils.
The map below shows how lopsided our impacts are.
Sources: Global Footprint Network , Project Drawdown
Click on a country to see its ecological deficit or reserve.
The majority of countries are running ecological deficits. These deficits occur when a population's total resource consumption exceeds the biological capacity of their area. A national ecological deficit means a nation is importing biocapacity through trade, liquidating ecological assets, or emitting carbon dioxide waste into the atmosphere. Example: The United States has abundant natural resources (biocapacity), but its high rate of consumption outstrips that capacity—thus the deficit.
Only about 50 countries, meanwhile, have ecological reserves, meaning their biocapacity exceeds their population's consumption.
Source: Global Footprint Network ( data )
Carbon dioxide levels in the atmosphere are at their highest in 15 million years.
Ice sheets in Greenland and Antarctica have trapped samples of ancient atmospheres. Extracting and analyzing ice cores reveals a pulsing, planetary heartbeat that shows how carbon dioxide levels have waxed and waned with the ice ages...until now.
Sources: NASA , Science Daily
In the planetary equivalent of the blink of an eye, humans have supercharged the atmosphere with heat-trapping CO₂. We've barely begun to see the impacts of our unintentional—and dangerous—planet-wide experiment.
Source: NASA
C O N S E Q U E N C E S
The Earth's average temperature has risen 1.8 degrees Fahrenheit (1 degree Celsius) since 1880.
With the exception of 1998, 18 of the 19 warmest years in the 136-year record all have occurred since 2001.
Source: NASA/GISS
Graphing average global surface temperature relative to the 1951-1980 average reveals a striking, undeniable planet-wide warming. That this trend will continue into the future is without doubt; the question is whether greenhouse gas emissions can be reduced rapidly enough to avoid catastrophic impacts on croplands, cities, and ecosystems.
The map shows projected temperature change by 2050, assuming global emissions are not curtailed. The Arctic will suffer the greatest temperature increases. Large swathes of Russia, Canada, and Alaska could warm by over 9°F (5°C).
Global warming is exacerbating economic inequality.
A 2019 Stanford University study found that, from 1961 to 2010, global warming decreased the wealth per person in the world’s poorest countries by 17 to 30 percent. In addition, the gap between the groups of nations with the highest and lowest economic output per person is now approximately 25 percent larger than it would have been without climate change.
For the most part, wealthier countries are in Earth's temperate zones, where temperature increases have a less severe impact—and can even be beneficial. "In cold countries," according to the study's lead author, "a little bit of warming can help. The opposite is true in places that are already hot.”
Climate change, as with many natural phenomena, has a greater adverse impact on marginalized populations. The affluent people who are responsible for the bulk of greenhouse gas emissions are suffering far less from their impacts than low-income populations that tend to be comprised of minorities.
Source: Stanford University
Global sea levels have risen eight inches in the past century.
Retreating ice sheets, induced by the global temperature spike, are causing sea levels to rise. The rate of change in the last two decades is nearly double that of the last century and is accelerating decade by decade.
Source: NASA
Number of people in major coastal cities exposed to flooding
Sea level rise and increased flooding from coastal storms is putting millions of people at risk. This map shows the twenty cities with the largest populations exposed to coastal flooding.
By 2070, more than 100 million people are projected to be vulnerable to flooding in these cities alone.
See NOAA's Coastal Flooding story
Ocean surface acidity has increased by about 30 percent since the beginning of the industrial revolution.
As humans emit more carbon dioxide into the atmosphere, increasing amounts of CO₂ filter into the oceans. Every year, about two billion additional tons of carbon dioxide are absorbed by the upper layer of the oceans.
The result is that seawater becomes more acidic. Among the effects: Mollusks and reef-building organisms that are key to the health of marine ecosystems become increasingly unable to build their shells, threatening their survival.
Change in ocean surface acidity, 1861-2018. Lighter areas = more change. Source: NOAA Science on a Sphere
Source: NASA
If current trends continue, up to 90 percent of Earth’s coral reefs may be gone by mid-century. Corals face a double threat: warming sea surface temperatures and increased acidity.
Rising temperatures have caused a dramatic increase in coral bleaching events. Lighter hues on the map below represent greater current risk of coral bleaching.
NOAA Coral Reef Watch map of reefs at risk.
Within the billions of tiny coral animals that build vast reef systems are symbiotic algae. When temperatures spike, the algae are expelled by the corals, turning them a ghostly white. Corals can survive a handful of these events, but repeated bleaching is fatal.
The loss of these diverse and productive reefs will have a devastating impact on marine ecosystems—and the millions of people whose livelihoods depend on them.
Source: WWF Living Planet Report
Every 10 years the extent of Arctic sea ice in September declines by 12.8 percent.
Arctic sea ice reaches its minimum extent each September. That extent is declining at a rate of 12.8 percent per decade relative to the 1981-2010 average.
The graph above shows the average monthly Arctic sea ice extent each September since 1979, derived from satellite observations. The 2012 extent is the lowest yet recorded. The animation below is based on satellite observations and shows minimum Arctic ice extent since 1979.
Source: NASA
Vertebrate animal populations declined on average by 58 percent between 1970 and 2012.
Less than half of the populations of animals with backbones that existed in 1970 remained in 2012—and declines continue. The biggest declines are in freshwater vertebrates: On average, they have shown an 81 percent decline in that time period.
Source: WWF Living Planet Report
Not only are animal populations declining, but whole species are going extinct. More than 26,000 known species are threatened with extinction. Species extinction rates are 100 to 1000 times higher than normal or “background” levels.
A quarter of mammal species are threatened with extinction, as is about one in seven bird species. And more than a third of amphibian species face potential extinction.
Climate change as "threat multiplier"
The impacts of climate change are distributed unevenly. That's true geographically—temperatures are increasing more in the Arctic than for the planet as a whole—and it's true demographically as well.
The disadvantaged, the disenfranchised, the underprivileged will suffer—and are suffering—far more from the impacts of a warming climate than affluent people who can afford to be more insulated from them. Fundamental issues such as poverty, hunger, lack of access to clean water, and availability of health care are all made more severe by climate change.
The sad irony is that those of us who are wealthier are contributing the most to the warming climate, yet are suffering its effects the least.
C O N S E N S U S
One hundred percent of actively publishing climate scientists agree: It is extremely likely that climate-warming trends over the past century are due to human activities.
A review of more than 11,000 research papers published in the first seven months of 2019 indicated that the scientific consensus had grown to 100%. A long-term consensus among scientists has now reached unanimity.
Previously, a group of 1,300 independent scientific experts from countries all over the world, under the auspices of the United Nations, had concluded there's a more than 95 percent probability that human activities over the past 50 years have warmed our planet.
This graph summarizes a series of studies gauging the degree of consensus within the scientific community on human-induced climate change. The consensus among scientists is overwhelmingly that human activities are the primary cause of climate change.
A C T I O N
We all need to take action.
Climate change isn't the fault of some distant villain. All of us contribute to the greenhouse gas emissions that are changing Earth's climate. And all of us can help alleviate the problem. Here are a few things that you can do.
Speak out
As climate scientist Katharine Hayhoe says, "Talk about it. Advocate for change at every level from your family to your school or business or organization to your elected representatives." As much as we can work as individuals to reduce our climate impact, governments and large corporations have a far greater effect on climate—and will be much more likely to make reforms if we put pressure on them.
Calculate your carbon footprint
A key first step in helping reduce your impact on the Earth is to assess the size of your impact. Several organizations offer lists or, better yet, step-by-step online questionnaires that make it easy to estimate your footprint. One of the better ones is the University of California's CoolClimate Calculator .
Reduce your carbon footprint
A number of reputable non-profits provide lists of steps you can take to reduce your personal and household footprint. Global Stewards offers a list of Top 20 Ways to Reduce Your Carbon Footprint .
Offset your carbon emissions
One way to alleviate your impact is to contribute to efforts, such as renewable energy projects, that are reducing overall levels of carbon emissions. This article by the Natural Resources Defense Council discusses the pros and cons of carbon offsets. Conserve Energy Future lists 11 Best and Popular U.S. Offset Providers .
Donate, join, or volunteer to organizations
Hundreds of organizations are mobilizing to tackle the many issues related to climate change and sustainability. Project Drawdown gathers and facilitates a broad coalition of researchers, scientists, policy makers, business leaders and activists to assemble and present the best available information on climate solutions. 350.org seeks to reduce atmospheric CO2 levels. The Nature Conservancy protects biodiversity by preserving key lands and waters. World Wildlife Fund and the Wildlife Conservation Society work to protect wildlife in a changing world.
