Given the weight of the evidence, scientists have come to a consensus that climate change is happening, and that human greenhouse gas emissions are the primary cause. There are still a lot of questions left about how fast climate change will happen and what the precise effects will be. One of the major unknowns is the ultimate influence of clouds on climate : Clouds are white, so they reflect sunlight back toward space, which could have a cooling effect.
But clouds are also water vapor, which traps heat. And different types of clouds might have warming or cooling effects, so the precise role of clouds in the feedback loop of global warming remains difficult to untangle , scientists have said. Another burning question is how high, and how quickly, the sea level will rise as warming sea waters expand and Antarctic and Arctic ice melts.
The IPCC forecasted a rise of 20 to 38 inches 52 to 98 cm , assuming no efforts are made to curb greenhouse gas emissions. That range is broad, largely because the dynamics of Antarctic ice sheets are not completely understood. If Antarctica's land-based glaciers slough off to the sea rapidly with a little bit of warming, that will be bad news for coastal communities, researchers have said.
That's why scientists are watching closely right now as a rift is splitting the Larsen C ice shelf on the Weddell Sea. If the giant iceberg-calving event about to occur destabilizes the ice shelf, it could result in the rapid flow of the land-based glaciers behind it into the ocean. This type of rapid glacial flow already occurred nearby, when the Larsen B ice shelf crumbled in For an ecologist like Moore Powell, there are also myriad questions to answer about how ecosystems will respond to a changing climate.
If the pace is slow enough, plants and animals can adapt. But in many places, the change is happening very quickly, Moore Powell said. Original article on Live Science. Gases, such as water vapor, which respond physically or chemically to changes in temperature are seen as "feedbacks. On Earth, human activities are changing the natural greenhouse. Over the last century the burning of fossil fuels like coal and oil has increased the concentration of atmospheric carbon dioxide CO 2.
This happens because the coal or oil burning process combines carbon with oxygen in the air to make CO 2. To a lesser extent, the clearing of land for agriculture, industry, and other human activities has increased concentrations of greenhouse gases. The consequences of changing the natural atmospheric greenhouse are difficult to predict, but some effects seem likely:.
Outside of a greenhouse, higher atmospheric carbon dioxide CO 2 levels can have both positive and negative effects on crop yields. Some laboratory experiments suggest that elevated CO 2 levels can increase plant growth.
However, other factors, such as changing temperatures, ozone, and water and nutrient constraints, may more than counteract anypotential increase in yield. If optimal temperature ranges for some crops are exceeded, earlier possible gains in yield may be reduced or reversed altogether. Since the start of the Industrial Revolution, the pH of the ocean's surface waters has dropped from 8.
This drop in pH is called ocean acidification. A drop of 0. A change of 0. Increasing acidity interferes with the ability of marine life to extract calcium from the water to build their shells and skeletons. That little bit of extra sunlight caused a little bit of warming. As the oceans warmed, they outgassed carbon dioxide—like a can of soda going flat in the heat of a summer day. The extra carbon dioxide in the atmosphere amplified the initial warming.
Based on air bubbles trapped in mile-thick ice cores and other paleoclimate evidence , we know that during the ice age cycles of the past million years or so, carbon dioxide never exceeded ppm. Before the Industrial Revolution started in the mids, the global average amount of carbon dioxide was about ppm. The amount of carbon dioxide in the atmosphere blue line has increased along with human emissions gray line since the start of the Industrial Revolution in Emissions rose slowly to about 5 billion tons per year in the mid th century before skyrocketing to more than 35 billion tons per year by the end of the century.
By the time continuous observations began at Mauna Loa Volcanic Observatory in , global atmospheric carbon dioxide was already ppm. On May 9, , the daily average carbon dioxide measured at Mauna Loa surpassed ppm for the first time on record. Less than two years later, in , the global amount went over ppm for the first time. If global energy demand continues to grow and to be met mostly with fossil fuels, atmospheric carbon dioxide is projected to exceed ppm by the end of this century.
Carbon dioxide emissions by country over time. Comparing greenhouse gases by their global warming potential. Collins, M. Knutti, J. Arblaster, J. Dufresne, T. Fichefet, P. Friedlingstein, X. Similarly, cloudy nights tend to be warmer than clear nights because more water vapor is present.
The influence of carbon dioxide can be seen in past changes in climate. Ice cores from over the past million years have shown that carbon dioxide concentrations were high during warm periods — about 0. During ice ages, when the Earth was roughly 7 to 13 F C cooler than in the 20th century, carbon dioxide made up only about 0. Even though water vapor is more important for the natural greenhouse effect, changes in carbon dioxide have driven past temperature changes.
In contrast, water vapor levels in the atmosphere respond to temperature. We take pills that are a tiny fraction of our body mass and expect them to affect us. Today the level of carbon dioxide is higher than at any time in human history. Without action to control emissions, carbon dioxide might reach 0. Without action, this little sliver of the atmosphere will cause big problems.
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