A Pew Research Center survey, released last week as part of a broader report on science and society, found that only 50 per cent of Americans believe that humans are mostly responsible for climate change, while 87 per cent of scientists accept this view. This 37-point gap persists even though thousands of scientists during the past few decades have been involved in publishing detailed reports linking climate change to carbon emissions.
Evidence of a human role in climate change keeps piling up. Recent studies of record-breaking temperatures, rising sea levels, and high levels of heat-trapping carbon dioxide in the atmosphere all point to an Earth under stress from a rapidly expanding human presence.
We are burning record levels of coal, oil, and natural gas to fuel modern society. As a result, we are producing record levels of greenhouse gases that warm the atmosphere, melt the planet's ice, and cause the oceans to become more acidic-threatening marine life.
And as our numbers and appetites keep growing, we also keep cutting down tropical forests to expand cropland and decimating native ocean fish populations with industrial-scale fishing. We pollute waterways and coastal regions with nitrogen and phosphate fertilizer runoff from those croplands.
Scientists say it's as if the gauges on Earth's environmental dashboard are flashing yellow and red as we put the planet under increasing stress.
In mid-January, researchers from the National Oceanic and Atmospheric Administration (NOAA) and NASA reported that 2014 was the warmest year in the past 135 years of record-keeping. Globally, land and ocean temperatures were 1.24?F (0.69?C) higher than the average for the 20th century-passing previous highs set in 2005 and 2010.
Temperatures have been rising for several decades, and with the exception of 1998, the ten warmest years since modern record-keeping began in 1880 have all been since 2000. The last time the Earth set an annual record for cold, according to NOAA, was 103 years ago in 1911.
'This is the latest in a series of warm years in a series of warm decades,' said Gavin Schmidt of NASA. 'While the ranking of individual years can be affected by chaotic weather patterns, the long-term trends are attributable to drivers of climate change that right now are dominated by human emissions of greenhouse gases.'
One striking, visible effect of rising temperatures is the shrinking Arctic ice cap. Satellites have been observing the ice cap since 1979 and since then the summer ice there has been shrinking about 12 per cent per decade. By the end of summer 2012, about half of the Arctic ice area present in 1979 had melted. National Geographic revised its most recent atlas to show this loss of Arctic ice.
National Geographic cartographer Juan José Valdés has said that, compared with previous editions, this remapping of the Arctic is 'the biggest visible change [on the world map] other than the breakup of the USSR.'
The coming flood
A new study says seas have been rising faster in the past two decades than anyone realized previously.
Seas are rising because ice sheets in Greenland and parts of Antarctica, and glaciers in Alaska and elsewhere, are melting as global temperatures rise. Meltwater flows from continents into the oceans, just like water flowing into a bathtub. Seawater also expands because it's getting hotter as global temperatures rise.
As Laura Parker reports in the February issue of National Geographic magazine, Miami and its suburbs face more financial risk from flooding due to sea-level rise by 2050 than any other major urban area in the world. By century's end, Miami could be dealing with seas up to five feet higher than now. It is one of many low-elevation coastal cities confronting the reality-and expense-of rising seas as salt water floods streets and intrudes into drinking water supplies.
This year began with atmospheric levels of carbon dioxide at 400 parts per million. Carbon dioxide, which comes from power plant smokestacks and vehicle tailpipes when we burn coal and gas or from forests when we burn them, has been flirting with this level since 2013.
Once carbon dioxide is in the sky, it stays up there for hundreds, even thousands of years, and it traps radiant or reflected solar heat in the atmosphere in a similar way as more blankets on our bed make us warmer. We have in effect been adding more blankets to Earth's atmosphere.
Carbon dioxide levels are more than one-third higher than they were at the start of the Industrial Revolution around 1750, and higher than they have been in 800,000 years or longer. Scientists know this because they have been pulling long cores from ice sheets in Greenland and Antarctica that have trapped in them ancient bubbles of carbon dioxide. Their studies indicate that when carbon dioxide levels are high, so are global temperatures.
We are on the verge of learning much more about how carbon dioxide-which serves as a global thermostat-works in the atmosphere. A new satellite carbon observatory called OCO-2, launched in 2014 by NASA's Jet Propulsion Laboratory, is starting to monitor Earth's carbon levels, and the goal is to map carbon dioxide circulation globally, showing its sources and how it moves throughout the year.
Besides trapping heat in the atmosphere, carbon dioxide also alters ocean chemistry. As oceans absorb it, they become more acidic, affecting the health of shelled organisms such as oysters, mussels, and coral reefs. Ocean acidification has been called global warming's 'evil twin.'
Another recent study reports that acidification, overfishing, seabed mining, and other human activities threaten the future of ocean life. One author of that study, Stephen Palumbi of Stanford University, told the New York Times that slowing extinctions in the oceans will require cutting back on carbon emissions.
'If by the end of the century we're not off the business-as-usual [carbon emissions] curve we are [on] now, I honestly feel there's not much hope for normal ecosystems in the ocean,' Palumbi said.
Keeping carbon down
If we want to keep carbon dioxide levels (and temperatures and sea levels) down, we need to rein in burning of things that cause CO2 levels to rise. At least that's the thinking of scientists studying reserves of coal, oil, and natural gas in the ground.
They are trying to determine how much of these carbon-rich fuels we must avoid burning to keep global temperatures from rising more than 3.6?F (2?C). This 3.6-degree level is considered a threshold beyond which we'll likely see rapid melting of ice sheets and even more rapid sea-level rise.
Researchers project in a new study that we must leave 80 per cent of the coal, 50 per cent of the natural gas, and 30 per cent of the oil in the ground to limit temperature increases. This is a hard sell for a world heavily reliant on these fuels. The US Department of Energy projects that coal, oil, and gas likely will remain the energy sources of choice for the United States for the next 25 years, and globally our reliance on coal and oil keeps rising.
Our tight embrace of fossil fuels and our expanding footprint across the planet has other impacts on oceans, landscapes, the atmosphere, and ecosystems.
New research from the Stockholm Resilience Centre looks at Earth as an integrated system containing a set of interlocking systems with 'boundaries.' These boundaries identify a 'safe operating space' for human beings measured by a set of gauges-just like in your car-called a 'planetary dashboard.'
These boundaries set theoretical limits on how much we can change the environment before the Earth systems that provide us food, clean water, and clean air, among other things, are themselves damaged. The study says we already have crossed planetary boundaries in four areas: extinction rates, deforestation, level of carbon dioxide in the atmosphere, and flow of nitrogen and phosphorus (used on land as crop fertilizer) into the ocean.
The researchers conclude that as we keep cutting down forests, domesticating wild lands, building more cities, depleting groundwater, polluting the air and water, and harvesting the oceans, we risk destroying the 'safe space for humanity' we have enjoyed for more than ten thousand years. The authors say their study amounts to an early warning system to help society 'reduce risk and develop sustainably.'
Dennis Dimick is National Geographic's Executive Editor for the Environment