There’s no mistake, according to the United Nations Intergovernmental Panel on Climate Change (IPCC): Humans are responsible for the bulk of the shifting environmental realities that we call climate change. If we do not alter our greenhouse-gas-emitting habits, the international body warned last week, Mother Earth may very well warm to a point that makes it difficult to support the very life that depends on it.
Last week’s report, Climate Change 2013: the Physical Science Basis, contained a number of alarming findings, all pointing to human activity as the main agent of climate change. Also included was a 36-page document for policymakers with bullet points listing the main climate trends and touching on their interplay.
Though it is cloaked in science-speak, the message is unmistakable.
“Human influence on the climate system is clear,” the IPCC said. “Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes.”
Absent behavioral and policy changes globally, the U.N. said, the trends will continue on their trajectories through the end of the century, while exacerbating and feeding off one another to compound the process.
Here are the major, scariest findings announced by the climate change panel. Although it seems, as some critiques have pointed out, to tell us what we already know, this latest report filters the data through vastly improved climate models and has put forth four scenarios based on different variables. They all add up to the same thing.
There is no question that the climate system is warming, with the most marked, unprecedented changes occurring since the 1950s, the IPCC said. In the Northern Hemisphere alone, the years 1983–2012 were most likely the warmest three decades in the past 1,400 years—since 600 A.D., as renowned climate scientist Piers Forster tweeted in summarizing the key findings, as compiled by the website Responding to Climate Change.
Most likely, the IPCC said, global surface temperatures will surpass preindustrial levels by 2.7 degrees Fahrenheit before the end of the 21st century. Greenhouse gas emissions will determine whether they will exceed the years 1986–2005 by 0.54 degrees or a whopping 8.64 degrees, the news website Climate Central said. And it’s all interconnected.
“The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased,” the IPCC said.
As the atmosphere has warmed, the ocean has absorbed much of that energy, the IPCC said. In fact, it soaked up at least 90 percent of the energy that accumulated between 1971 and 2010, the report calling it “virtually certain” that the upper ocean warmed between those years and probably had been doing so since the 1870s.
The ocean’s surface and upper layers have heated up the most, the report said, but that is expected to reach greater and greater depth as the century wears on. This could very well affect ocean circulation, tampering with what is known as the global conveyor belt—the movement of water around the planet in a system regulated by temperature and salinity, as described by the National Atmospheric and Oceanic Administration.
The ice is melting. Greenland and the Antarctic have both lost ice mass over the past two decades, while glaciers have shrunk. Arctic sea ice has also decreased, as has the spring snow cover in the Northern Hemisphere.
This not only raises sea level but also contributes to Earth’s warming. Higher temperatures change the balance of salinity in the water, which causes the ice to melt even faster. This melting ice is draining into the sea.
4. Sea Level
Melting ice and other factors have caused the global mean sea level to rise by 0.19 meters. Turtle Island, especially in the Northeast, will bear the brunt of this initially, especially when it comes to storm surge.
What does this mean on the ground? It depends both on elevation and the composition of the terrain, notes Climate Central. Effects would be minimal along parts of the California coast that rise sharply out of the sea, while flat coastal areas such as Miami would see the water encroaching almost immediately, Climate Central says in its Surging Seas project. And places such as New Orleans, below sea level, will see the basic water level rise markedly.
That is the water part. There’s also the ground. Again, in Florida, that even-with-sea-level existence is lived atop porous bedrock, giving rising salt water the chance to infiltrate freshwater aquifers near the coast, Climate Central said. In addition, rivers and canals will have trouble draining into the ocean, overfull as it is. This will become especially apparent during rainstorms, as these conduits overflow their banks.
And speaking of storms, a higher sea level means a higher threshold that gets rain dumped on it during an extreme weather event such as a hurricane, Climate Central said. Last year’s Superstorm Sandy was a prime example of that, flooding parts of New York City as it did.
5. Carbon and Greenhouse Gases
Carbon dioxide concentrations in the atmosphere, along with methane and nitrous oxide, “have increased to levels unprecedented in at least the last 800,000 years,” the IPCC report said. Carbon dioxide alone has increased by 40 percent over pre-industrial times, mainly because of fossil fuel emissions.
“Continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system,” the report said. “Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.”
Carbon issues are not limited to atmospheric concentrations, the report pointed out. Not all of it goes into the air. Some goes into the ocean, acidifying the water and making it difficult to support marine life. Eroding coral is just one example.
Quite simply, these trends could compromise our very existence, climate scientists said upon releasing the report on Friday September 27.
“Climate change challenges the two primary resources of humans and ecosystems—land and water,” said Thomas Stocker, a climate scientist at the University of Bern in Switzerland and one of the leaders of the IPCC’s Working Group I, which authored the report. “In short, it threatens our planet, our only home.”