Simple Answers to 13 Complex Climate Questions

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Clearing the Air on Climate Change

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As stewards of the Earth we are responsible for its health. Yuri_Arcurs/DigitalVision/Getty Images

Weather may be a topic of polite conversation, but climate and climate change is one of controversy -- controversy that only clouds the true science of the issue. Hoping to sift through the opinions of skeptics and fanatics to find and understand the truth? Start by exploring these top climate change questions and answers.


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How much has Earth warmed?

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From 1880 (when we began tracking global temperatures) to 2015, Earth has warmed by about 1.7°F (+0.9°C).

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Warming by 1.7 degrees doesn't sound significant. Why should I be concerned?

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If your outdoor air temperature warmed or fell by 1.7 degrees, you're right, you probably wouldn't notice it. But over the surface of an entire planet, this seemingly small amount is actually quite significant.

Consider this: global temperatures at the end of the last ice age (when the Northeast U.S. was covered by thousands of feet of ice) were only 5°F to 9°F cooler than they are today. So you can see why the almost 2 degree increase we've already experienced is cause for concern.

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Weren't temperatures warmer in past climates than they are today?

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It's true, during the period between 950 to 1250 (a time known as the Medieval Warm Period) there were temperatures Earth was as warm or warmer than it is now. Some use this to justify and rationalize today's rising temperatures, but there are two reasons why this argument simply doesn't hold water.

For one, the warmth of the Medieval Warm Period was prevalent in the Northern Hemisphere (especially Greenland, Europe and parts of Asia) -- not worldwide like the warming of today. Secondly, the Medieval Warm Period can be explained by natural changes in the environment -- like increased solar activity and a lack of volcanic activity -- whereas the warming of today is driven by the unnatural pumping of greenhouse gases like carbon dioxide (CO2) into the air at rates faster than nature has ever done. You can't take two vastly different scenarios like the Medieval Warm Period and today's modern climate and use one as a guide for what will happen with the other. It's just not good science.

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How much warmer will Earth get?

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According to the Fifth Report of the Intergovernmental Panel on Climate Change (IPCC), if we do nothing to curb carbon dioxide emissions, scientists project global temperatures will likely warm 8.6°F (+4.8°C) by the years 2081 to 2100.

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How do scientists make predictions about our future climate? Are these reliable?

sick earth climate change
Climate models give scientists a "best guess" of how our climate might change in the future. Fanatic Studio/Getty Images

No one knows for certain what our future climate will look like. But much like meteorologists use forecast models to predict the weather based on current conditions, climate scientists use climate models to do the same. It works like this: a range of starting scenarios (such as varying emissions level values) are fed into the climate models -- computer programs that use mathematical equations to simulate how the atmosphere and oceans might respond to each scenario. The model then "runs," or solves the equations for those specific conditions. Each model run solution represents a possible climate outcome.

While climate models are one of the best tools for making climate projections, they aren't perfect. This is why scientists have begun using the language likely, very likely, extremely likely, medium confidence, and high confidence in reports when speaking about climate outcomes.

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How do we know our climate is changing?

polar bear jumps on sea ice
As of 2008, the polar bear has been placed on the "threatened species" list due to the decline of its habitat, Arctic sea ice, as a result of global warming. Danita Delimont/Gallo Images/Getty Images

Signs that Earth's climate is warming include:

  • Warming temperatures
  • Warming oceans
  • Sea level rise (As land ice melts, water is added to our oceans. Sea water also expands in volume as it warms.) 
  • Shrinking ice sheets
  • Declining arctic sea ice
  • Glacial retreat
  • Decreased snow cover
  • Ocean acidification (Roughly 30-40% of CO2 released into the atmosphere dissolves in rivers, lakes, and oceans where it forms carbonic acid. This increased acidity stresses marine life and leads to diseases like coral bleaching.)
  • An increase in extreme weather events

While these changes aren't unique to today's warming (they've been observed in the past) what is unique is that they're happening at alarmingly rapid rates. For example, the rate of sea level rise over the last 10 years (3.41 mm per year) is nearly double that we've recorded over the last 100 years (1.54 mm per year).

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If the world is warming, why are some winters still very cold and snowy?

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Global warming is a long-term trend. This doesn't mean that every year will be warmer than the previous one, or that we will no longer have unusually cold days, nights, winters, or winter storms. (In fact, some regions may experience heavier snowfall during winter since in a warmer world, the air is able to hold more moisture, thus leading to heavier precipitation events.)

What it does mean is that, on a global scale, the number of record-breaking cold days, nights, and winters is likely to decrease while warm temperature extremes are expected to increase. Evidence of this has already been seen.

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Why is carbon dioxide a "main suspect" of climate change?

CO2 emissions illustration
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Carbon dioxide is a heat-trapping gas. At natural levels, it helps keep the atmosphere warm enough for us to live on Earth, but at excess levels it warms the planet beyond comfort. 

While other greenhouse gases like methane, nitrous oxide, CFCs, and water vapor are more powerful at trapping heat than carbon dioxide, CO2 is of greatest concern because (1) it is present in much larger concentrations, and (2) it "lives" in the atmosphere for far longer. Carbon dioxide can remain in the air anywhere from several decades to thousands of years. In comparison, nitrous oxide stays in the air for roughly 121 years; methane, roughly 12.5 years; and water vapor, hours to days only (since it is rapidly removed as rain and snow).

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What proof exists that humans DO contribute to global warming?

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It is extremely likely that over half of the global surface temp increase seen from 1951-2010 is human-caused. IPCC

For one, paleoclimate data show that the climb in levels of carbon dioxide in the atmosphere coincide with the Industrial Revolution -- society's transition to chemical and mechanical manufacturing. (For centuries (going back as far as 400,000 years before, never rose above 300 ppm.)

Secondly, it's a fact that natural processes alone cannot explain the warming we've observed over the past 100 years. This image shows the actual warming trend in temperatures (black bar) versus how they should have warmed if we consider natural factors only, like how much energy from the sun reaches Earth (purple bar). The orange bar represents the expected temperature change from "anthropogenic" or human activities, like burning of fossil fuels and deforestation. As you can clearly see, the black almost mirrors the orange, which undeniably suggests that human causes win out.

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How has human activity disturbed the natural carbon cycle?

power plant smoke
Don't let the smoke color fool you! Power stations are responsible for nearly 40% of CO2 emissions in the U.S. Claudia Otte/Moment/Getty Images

We humans add CO2 into the atmosphere through the combustion of fossil fuels (coal, natural gas, and oil) -- but not just through cars, planes, and trains. Sure, burning gasoline and diesel to transport people, food, and goods is a significant (30%) source of CO2 emissions within the U.S. However, the largest single source -- nearly 40% -- comes from using fossil fuels to generate electricity for our homes and businesses.

More: What is a contrail cloud?

Another way we contribute to CO2 buildup in the atmosphere is by deforestation or clearing lands of plants and trees, which are able to absorb CO2 from the air and store it.

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Is there a point at which adding more CO2 will not cause further warming?

carbon dioxide sunrise
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No. As long as more CO2 is added to the atmosphere, average global air temperatures will continue to rise. Because what CO2 does is trap heat, the more CO2 there is, the more and more heat it will trap.


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Can climate change be stopped?

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Unfortunately, we can't stop or reverse the changes that have already occurred in our climate system, but we may be able to "mitigate" or slow global warming. Scientists project that if the world limits the carbon dioxide it has emitted since the Industrial Revolution to 1 trillion tons (1,000 PgC) it can likely limit warming to 3.6°F (2°C). (As of 2011, we've already emitted 515 PgC.) In order to meet this target, annual global emissions would need to peak by the year 2020 and then fall by 50% of that level by the year 2050. 

The Paris Climate Pact of 2015 is the first universal agreement to set this goal. The agreement will become legally binding if at least 55 countries sign it between Earth Days 2016 and 2017. 

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Where can I keep up with the latest climate news?

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For the latest climate news headlines and maps of various climate conditions, visit NOAA's portal.

Want climate details for a specific month or year? Explore NOAA's National Centers for Environmental Information (NCEI) State of the Climate reports for monthly and annual recaps of climate-related happenings on a national and global scale.

For full scientific and technical findings within the climate field, you'll want to browse the Intergovernmental Panel on Climate Change (IPCC) climate assessment reports. Published every 5 to 6 years, the latest version available is the Fifth Assessment Report (AR5) of 2014.


Resources & Links:

IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

NASA Global Climate Change: Vital Signs of the Planet.