Climate Change: Evidence and Causes Flashcards
Is the climate warming?
Yes. Earth’s average surface air temperature has increased by about 1 °C (1.8 °F) since 1900, with over half of the increase occurring since the mid-1970s. A wide range of other observations (such as reduced Arctic sea ice extent and increased ocean heat content) and indications from the natural world (such as poleward shifts of temperature-sensitive species of fish, mammals, insects, etc.) together provide incontrovertible evidence of planetary-scale warming.
How do scientists know that recent climate change is largely caused by human activities?
Scientists know that recent climate change is largely caused by human activities from an understanding of basic physics, comparing observations with models, and fingerprinting the detailed patterns of climate change caused by different human and natural influences.
CO2 is already in the atmosphere naturally, so why are emissions from human activity significant?
Human activities have significantly disturbed the natural carbon cycle by extracting long-buried fossil fuels and burning them for energy, thus releasing CO2 to the atmosphere.
What role has the Sun played in climate change in recent decades?
The Sun provides the primary source of energy driving Earth’s climate system, but its variations have played very little role in the climate changes observed in recent decades. Direct satellite measurements since the late 1970s show no net increase in the Sun’s output, while at the same time global surface temperatures have increased.
What do changes in the vertical structure of atmospheric temperature —from the surface up to the stratosphere—tell us about the causes of recent climate change?
The observed warming in the lower atmosphere and cooling in the upper atmosphere provide us with key insights into the underlying causes of climate change and reveal that natural factors alone cannot explain the observed changes.
Climate is always changing. Why is climate change of concern now?
All major climate changes, including natural ones, are disruptive. Past climate changes led to extinction of many species, population migrations, and pronounced changes in the land surface and ocean circulation. The speed of the current climate change is faster than most of the past events, making it more difficult for human societies and the natural world to adapt.
Is the current level of atmospheric CO2 concentration unprecedented in Earth’s history?
The present level of atmospheric CO2 concentration is almost certainly unprecedented in the past million years, during which time modern humans evolved and societies developed. The atmospheric CO2 concentration was however higher in Earth’s more distant past (many millions of years ago), at which time palaeoclimatic and geological data indicate that temperatures and sea levels were also higher than they are today.
Is there a point at which adding more CO2 will not cause further warming?
No. Adding more CO2 to the atmosphere will cause surface temperatures to continue to increase. As the atmospheric concentrations of CO2 increase, the addition of extra CO2 becomes progressively less effective at trapping Earth’s energy, but surface temperature will still rise.
Does the rate of warming vary from one decade to another?
Yes. The observed warming rate has varied from year to year, decade to decade, and place to place, as is expected from our understanding of the climate system. These shorterterm variations are mostly due to natural causes, and do not contradict our fundamental understanding that the long-term warming trend is primarily due to human-induced changes in the atmospheric levels of CO2 and other greenhouse gases.
Did the slowdown of warming during the 2000s to early 2010s mean that climate change is no longer happening?
No. After the very warm year 1998 that followed the strong 1997-98 El Niño, the increase in average surface temperature slowed relative to the previous decade of rapid temperature increases. Despite the slower rate of warming, the 2000s were warmer than the 1990s. The limited period of slower warming ended with a dramatic jump to warmer temperatures between 2014 and 2015, with all the years from 2015-2019 warmer than any preceding year in the instrumental record. A short-term slowdown in the warming of Earth’s surface does not invalidate our understanding of long-term changes in global temperature arising from human-induced changes in greenhouse gases.
If the world is warming, why are some winters and summers still very cold?
Global warming is a long-term trend, but that does not mean that every year will be warmer than the previous one. Day-to-day and year-to-year changes in weather patterns will continue to produce some unusually cold days and nights and winters and summers, even as the climate warms.
Why is Arctic sea ice decreasing while Antarctic sea ice has changed little?
Sea ice extent is affected by winds and ocean currents as well as temperature. Sea ice in the partly-enclosed Arctic Ocean seems to be responding directly to warming, while changes in winds and in the ocean seem to be dominating the patterns of climate and sea ice change in the ocean around Antarctica.
How does climate change affect the strength and frequency of floods, droughts, hurricanes, and tornadoes?
Earth’s lower atmosphere is becoming warmer and moister as a result of human-caused greenhouse gas emissions. This gives the potential for more energy for storms and certain extreme weather events. Consistent with theoretical expectations, the types of events most closely related to temperature, such as heatwaves and extremely hot days, are becoming more likely. Heavy rainfall and snowfall events (which increase the risk of flooding) are also generally becoming more frequent.
How fast is sea level rising?
Long-term measurements of tide gauges and recent satellite data show that global sea level is rising, with the best estimate of the rate of global-average rise over the last decade being 3.6 mm per year (0.14 inches per year). The rate of sea level rise has increased since measurements using altimetry from space were started in 1992; the dominant factor in global-average sea level rise since 1970 is human-caused warming. The overall observed rise since 1902 is about 16 cm (6 inches).
What is ocean acidification and why does it matter?
Direct observations of ocean chemistry have shown that the chemical balance of seawater has shifted to a more acidic state (lower pH) [Figure 7]. Some marine organisms (such as corals and some shellfish) have shells composed of calcium carbonate, which dissolves more readily in acid. As the acidity of sea water increases, it becomes more difficult for these organisms to form or maintain their shells.
