Climate Change: Your Questions About Causes and Effects, Answered

Climate Change: Your Questions About Causes and Effects, Answered

Reporters from the Climate Desk gathered reader questions and are here to help explain some frequent puzzlers.

Published Updated 


What’s one thing you want to know about climate change? We asked, and hundreds of you responded.

The topic, like the planet, is vast. Overwhelming. Complex. But there’s no more important time to understand what is happening and what can be done about it.

I understand that scientists believe that some extreme cold weather events are due to climate change, but I don’t quite understand how, especially if Earth is getting warmer overall. Could you explain this? — Gabriel Gutierrez, West Lafayette, Ind.

The connection between climate change and extreme cold weather involves the polar jet stream in the Northern Hemisphere, strong winds that blow around the globe from west to east at an altitude of 5 to 9 miles. The jet stream naturally shifts north and south, and when it shifts south, it brings frigid Arctic air with it.

A separate wind system, called the polar vortex, forms a ring around the North Pole. When the vortex is temporarily disrupted — sometimes stretched or elongated, and other times broken into pieces — the jet stream tends to take one of those southward shifts. And research “suggests these disruptions to the vortex are happening more often in connection with a rapidly warming, melting Arctic, which we know is a clear symptom of climate change,” said Jennifer A. Francis, a senior scientist at the Woodwell Climate Research Center.

In other words, as climate change makes the Arctic warmer, the polar vortex is being more frequently disrupted in ways that allow Arctic air to escape south. And while temperatures are increasing on average, Arctic air is still frigid much of the time. Certainly frigid enough to cause extreme cold snaps in places like, say, Texas that are not accustomed to or prepared for them.

Where the extreme cold occurs depends on the nature of the disruption to the polar vortex. One type of disruption brings Arctic air into Europe and Asia. Another type brings Arctic air into the United States, and “that’s the type of polar vortex disruption that’s increasing the fastest,” said Judah L. Cohen, the director of seasonal forecasting at Atmospheric and Environmental Research, a private organization that works with government agencies.

It is important to note that these atmospheric patterns are extremely complicated, and while studies have shown a clear correlation between the climate-change-fueled warming of the Arctic and these extreme cold events, there is some disagreement among scientists about whether the warming of the Arctic is directly causing the extreme cold events. Research on that question is ongoing.

What impact will climate change have on biodiversity? How are they interlinked? How do the roles of developing versus developed countries differ, for example the United States and India? — A reader in India

Warmer oceans are killing corals. Rising sea levels threaten the beaches that sea turtles need for nesting, and hotter temperatures are causing more females to be born. Changing seasons are increasingly out of step with the conditions species have evolved to depend on.

And then there are the polar bears, long a symbol of what could be lost in a warming world.

Climate change is already affecting plants and animals in ways that scientists are racing to understand. One study predicted sudden die offs, with large segments of ecosystems collapsing in waves. This has already started in coral reefs, scientists say, and could start in tropical forests by the 2040s.

Keeping global warming under 2 degrees Celsius, or 3.6 degrees Fahrenheit, the upper limit outlined by the Paris Agreement, would reduce the number of species exposed to dangerous climate change by 60 percent, the study found.

Despite these grim predictions, climate change isn’t yet the biggest driver of biodiversity loss. On land, the largest factor is the ways in which people have reshaped the terrain itself, creating farms and ranches, towns and cities, roads and mines from what was once habitat for myriad species. At sea, the main cause of biodiversity loss is overfishing. Also at play: pollution, introduced species that outcompete native ones, and hunting. A sobering report in 2019 by the leading international authority on biodiversity found that around a million species were at risk of extinction, many within decades.

While climate change will increasingly drive species loss, that’s not the only way in which the two are interlinked. Last year the same biodiversity panel joined with its climate change counterpart to issue a paper declaring that neither crisis could be addressed effectively on its own. For example, intact ecosystems like peatlands and forests both nurture biodiversity and sequester carbon; destroy them, and they turn into emitters of greenhouse gasses as well as lost habitat.

What to do? The science is clear that the world must transition away from fossil fuels far more quickly than is happening. Deforestation must stop. Consuming less meat and dairy would free up farmland for restoration, providing habitat for species and stashing away carbon. Ultimately, many experts say, we need a transformation from an extraction-based economy to a circular one. Like nature’s cycle, our waste — old clothes, old smartphones, old furniture — must be designed to provide the building blocks of what comes next.

Countries around the world are working on a new United Nations biodiversity agreement, which is expected to be approved later this year. One sticking point: How much money wealthy countries are willing to give poorer ones to protect intact natural areas, since wealthy countries have already largely exploited theirs.

Where is the trimmed back version of climate legislation at? Joe Manchin reportedly said he would support such a bill. What do you know about the bill and will it pass with just Democrats? — Richard Buttny, Virgil, N.Y.

What is the current stated U.S. goal regarding reducing greenhouse gases and climate change, and how likely is it that we will achieve that goal? What do we need to do today to make progress toward achieving that goal? — Kathy Gray, Oak Ridge, Tenn.

Richard, as to the last part of your question, honestly, at this point your guess is as good as ours.

But here is what we know so far. Senator Joe Manchin III, Democrat of West Virginia, the most powerful man in Congress because his support in an evenly divided Senate is key, effectively killed President Biden’s Build Back Better climate and social spending legislation when he ended months of negotiations last year, saying he could not support the package.

A few weeks ago amid talks of revived discussions, Mr. Manchin was blunt. “There is no Build Back Better legislation,” he told reporters. Mr. Manchin also has not committed to passing a smaller version of the original $1 trillion spending plan. He has, however, voiced support for an “all of the above” energy package that increases oil and gas development.

Democrats hope that billions of dollars in tax incentives for wind, solar, geothermal and electric vehicle charging stations can also make its way into such a package. But relations between the White House and Mr. Manchin are rocky and it is unclear whether such a bill could pass before lawmakers leave town for an August recess.

To your emissions question, Kathy, Mr. Biden has pledged to cut United States emissions 50 to 52 percent below 2005 levels by 2030. Energy experts say it is a challenging but realistic goal, and critical for helping the world avert the worst impacts of climate change.

It’s not going to be easy. So far there are few regulations and even fewer laws that can help achieve that target. Mr. Biden’s centerpiece legislation, the Build Back Better Act, includes $550 billion in clean energy tax incentives that researchers said could get the country about halfway to its goal. But, as noted, that bill is stalled in the Senate. Even if it manages to win approval this year, the administration will still have to enact regulations on things like power plants and automobile emissions to meet the target.

A lot of coverage on climate change deals with rising sea levels and extreme weather — droughts, floods, etc. My question is more about how climate change will affect drinking water and access to safe clean water. Are we in danger within our current lifetime to see an impact to safe water within the U.S. due to climate change? — Jessica, Silver Spring, Md.

Climate change threatens Americans’ access to clean drinking water in a number of ways. The most obvious is drought: Rising temperatures are reducing the snowpack that supplies drinking water for much of the West.

But drought is far from the only climate-related threat to America’s water. Along the coast, cities like Miami that draw drinking water from underground aquifers have to worry about rising seas pushing saltwater into those aquifers, a process called saltwater intrusion. And rising seas also push up groundwater levels, which can cause septic systems to stop working, pushing unfiltered human waste into that groundwater.

Even in cities far from the coast, worsening floods are overwhelming aging sewer systems, causing untreated storm water and sewage to reach rivers and streams more frequently. And some 2,500 chemical sites are in areas at risk of flooding, which could cause those chemicals to leach into the groundwater.

In some cases, protecting drinking water from the effects of climate change is possible, so long as governments can find enough money to upgrade infrastructure — building new systems to contain storm water, for example, or better protect chemicals from being released during a flood.

Far harder will be finding new supplies of water to make up for what’s lost as temperatures rise. Some communities are responding by pumping more water from the ground. But if those aquifers are depleted faster than rainwater can replenish them, they will eventually run dry, a concern with the Ogallala Aquifer that supports much of the High Plains.

Even with significant reductions in water use, climate change could reduce the number of people that some regions can support, and leave more areas dependent on importing water.

Why don’t we create a national acequia system to capture excess rain falling primarily in the Eastern United States and pipeline it to the drought in the West? Carol P. Chamberland, Albuquerque, N.M

The idea of taking water from one community and giving it to another has some basis in American history. In 1913, Los Angeles opened an aqueduct to carry water from Owens Valley, 230 miles north of the city, to sustain its growth.

But the project, in addition to costing some $23 million at the time, greatly upset Owens Valley residents, who so resented losing their water that they took to dynamiting the aqueduct. Repeatedly.

Today, there are some enormous water projects in the United States, though building a pipeline that spanned a significant stretch of the country would be astronomically more difficult. The distance between Albuquerque, for example, and the Mississippi River — perhaps the closest hypothetical starting point for such a pipeline — is about 1,000 miles, crossing at least three states along the way. Moving that water all the way to Los Angeles would mean piping it at least 1,800 miles across five states.

So the engineering and permitting challenges alone would be daunting. And that’s assuming the local and state governments that would have to give up their water would be willing to do so.

China dealt with similar challenges to build a colossal network of waterways that is transferring water from the country’s humid south to its dry north. But of course, China’s system of government makes engineering feats of that scale somewhat more feasible to pull off.

For the United States, it would be easier to just build a series of desalination plants along the West coast, according to Greg Pierce, director of the Human Right to Water Solutions Lab at the University of California, Los Angeles. And before turning to desalination, which is itself energy-intensive and thus expensive, communities in the West should work harder at other steps, such as water conservation and recycling, he said.

“It’s not worth it,” Dr. Pierce said of the pipeline idea. “You’d have to exhaust eight other options first.”

How can we have faith in climate modeling when extreme events are much worse than predicted? Given “unexpected” extreme events like the 2021 Pacific Northwest heat wave and extreme heat in Antarctica that appear to shock scientists, it’s difficult for me to trust the I.P.C.C.’s framing that we haven’t run out of time. — Kevin, Herndon, Va.

Climate scientists have said for a long time that global warming is causing the intensity and frequency of many types of extreme weather to increase. And that’s exactly what has been happening. But global climate models aren’t really designed to simulate extreme events in individual regions. The factors that shape individual heat waves, for instance, are very local. Large-scale computer models simply can’t handle that level of detail quite yet.

That said, sometimes there are events that seem so anomalous that they make scientists wonder if they reflect something totally new and unforeseen, a gap in our understanding of the climate. Some researchers put the 2021 Pacific Northwest heat wave in that category, and are working to figure out whether they need to re-evaluate some of their assumptions.

For its part, the I.P.C.C. has hardly failed to acknowledge what’s happening with extreme weather. But its mandate is to assess the whole range of climate research, which might make it lean toward the middle of the road in its summaries. A decade ago, when a group of researchers looked back at the panel’s assessments from the early 2000s, they found that it generally underestimated the actual changes in sea level rise, increases in surface temperatures, intensity of rainfall and more. They blamed the instinct of scientists to avoid making conclusions that seem “excessively dramatic,” perhaps out of fear of being called alarmist.

The panel’s latest report, from April, concluded that we haven’t run out of time to slow global warming, but only if nations and societies make some huge changes right away. That’s a big if.

Why are climate change scientists faceless, aloof, terrible communicators and absent from social media? — A reader in Dallas

Climate science may not yet have its Bill Nye or its Neil deGrasse Tyson, but plenty of climate scientists are passionate about communicating their work to the public. Lots of them are on Twitter. Here’s a (very small) cross-section of people to follow, in alphabetical order:

  • Alaa Al Khourdajie: Senior scientist in London with the Intergovernmental Panel on Climate Change, the body of experts convened by the United Nations that puts out regular, authoritative surveys of climate research. Tweets on climate change economics and climate diplomacy.

  • Andrew Dessler: Professor of atmospheric sciences at Texas A&M University. Elucidator of energy and renewables, climate models and Texas.

  • Zeke Hausfather: Climate research lead at the payment processing company Stripe and scientist at Berkeley Earth, a nonprofit research group. A seemingly tireless chronicler, charter and commentator on all things climate.

  • David Ho: Climate scientist at the University of Hawaii at Manoa and École Normale Supérieure in Paris. Talks oceans and carbon dioxide removal, with wry observations on transit, cycling and life in France, too.

  • Twila Moon: Deputy lead scientist at the National Snow and Ice Data Center in Boulder, Colo. Covers glaciers, polar regions and giant ice sheets, and why we should all care about what happens to them.

  • Maisa Rojas: Climatologist at the University of Chile and Chile’s current environment minister. Follow along for slices of life at the intersection of science and government policy.

  • Sonia I. Seneviratne: Professor of land-climate dynamics at ETH Zurich in Switzerland. Tweets on extreme weather, greenhouse gas emissions and European energy policy.

  • Chandni Singh: Researcher on climate adaptation at the Indian Institute for Human Settlements in Bangalore. Posts about how countries and communities are coping with climate change, in both helpful ways and not so helpful ones.

  • Kim Wood: Geoscientist and meteorologist at Mississippi State University. A fount of neat weather maps and snarky GIFs.

The world is trying to reforest the planet by planting nonnative trees like eucalyptus. Is this another disastrous plan? Shouldn’t they be planting native trees? — Katy Green, Nashville

Ecologists would say planting native trees is the best choice. We recently published an article on this very topic, examining how tree planting can resurrect or devastate ecosystems, depending on what species are planted and where.

To be sure, people need wood and other tree products for all kinds of reasons, and sometimes nonnative species make sense. But even when the professed goal is to help nature, the commercial benefits of certain trees, like Australian eucalyptus in Africa and South America or North American Sitka spruce in Europe, often win out.

A new standard is in development that would score tree planting projects on how well they’re doing with regard to biodiversity, with the aim of helping those with poor scores to improve.

The same ecological benefit of planting native species also holds true for people’s yards. Doug Tallamy, a professor of entomology at the University of Delaware, worked with the National Wildlife Federation to develop this tool to help people find native trees, shrubs and flowers that support the most caterpillars, which in turn feed baby birds.

Why are we not investing in scalable solutions that can remove carbon or reduce solar radiation? — Hayes Morehouse, Hayward, Calif.

As a group, these types of solutions are referred to as geoengineering, or intentional manipulation of the climate. Geoengineering generally falls into two categories: removing some of the carbon dioxide already in the atmosphere so Earth traps less heat, known as direct air capture, or reducing how much sunlight reaches Earth’s surface so that there is less heat to begin with, usually called solar radiation management.

There are a few companies developing direct air capture machines, and some have deployed them on a small scale. According to the International Energy Agency, these projects capture a total of about 10 thousand tons of CO2 a year, a tiny fraction of the roughly 35 billion tons of annual energy-related emissions. Removing enough CO2 to have a climate impact would take a long time and require many thousands of machines, all of which would need energy to operate.

The captured gas would also have to be securely stored to keep it from re-entering the atmosphere. Those hurdles make direct air capture a long shot, especially since, for now at least, there are few financial incentives to overcome them. No one wants to pay to remove carbon dioxide from the air and bury it underground.

Solar radiation management is a different story. The basics of how to do it are known: inject some kind of chemical (perhaps sulfur dioxide) into the upper atmosphere, where it would reflect more of the sun’s rays. Relatively speaking, it wouldn’t be all that expensive (a fleet of high-flying planes would probably suffice) although once started it would have to continue indefinitely.

The major hurdle to developing the technology has been grave concern among many scientists, policymakers and others about unintended consequences that might result, and about the lack of a structure to govern its deployment. To date, there have been almost no real-world studies of the technology.

One key finding of climate science is that global temperatures have increased by 2 degrees Fahrenheit since the late 1800s. How can we possibly have reliable measures of global temperatures from back then, keeping in mind that oceans cover about 70 percent of the globe and that a large majority of land has never been populated by humans to any significant degree? — Robert, Madison, Wis.

The mercury thermometer was invented in the early 1700s, and by the mid- to late 19th century, local temperatures were being monitored continuously in many locations, predominantly in the United States, Europe and the British colonies. By 1900, there were hundreds of recording stations worldwide, but over half of the Southern Hemisphere still wasn’t covered. And the techniques could be primitive. To measure temperatures at the sea’s surface, for instance, the most common method before about 1940 was to toss a bucket overboard a ship, haul it back up with a rope and read the temperature of the water inside.

To turn these spotty local measurements into estimates of average temperatures globally, across both land and ocean, climate scientists have had to perform some highly delicate analysis. They’ve used statistical models to fill in the gaps in direct readings. They’ve taken into account when weather stations changed locations or were situated close to cities that were hot for reasons unrelated to larger temperature trends.

They have also used some clever techniques to try to correct for antiquated equipment and methods. Those bucket readings, for example, might be inaccurate because the water in the bucket cooled down as it was pulled aboard. So scientists have scoured various nations’ maritime archives to determine what materials their sailors’ buckets were made of — tin, wood, canvas, rubber — during different periods in history and adjusted the way they incorporate those temperature recordings into their computations.

Such analysis is fiendishly tricky. The numbers that emerge are uncertain estimates, not gospel truth. Scientists are working constantly to refine them. Today’s global temperature measurements are based on a much broader and more quality-controlled set of readings, including from ships and buoys in the oceans.

But having a historical baseline, even an imperfect one, is important. As Roy L. Jenne, a researcher at the National Center for Atmospheric Research, wrote in a 1975 report on the institution’s collections of climate data: “Although they are not perfect, if they are used wisely they can help us find answers to a number of problems.”

Is the environmental damage collecting metals/producing batteries for electric cars more dangerous to the environment than gas powered vehicles? — Sandy Rogers, San Antonio, Texas

There’s no question that mining the metals and minerals used in electric car batteries comes with sizable costs that are not just environmental but also human.

Much of the world’s cobalt, for example, is mined in the Democratic Republic of Congo, where corruption and worker exploitation has been widespread. Extracting the metals from their ores also requires a process called smelting, which can emit sulfur oxide and other harmful air pollution.

Beyond the minerals required for batteries, electric grids still need to become much cleaner before electric vehicles are emissions free.

Most electric vehicles sold today already produce significantly fewer planet-warming emissions than most cars fueled with gasoline, but a lot still depends on how much coal is being burned to generate the electricity they use.

Still, consider that batteries and other clean technology require relatively tiny amounts of these critical minerals, and that’s only to manufacture them. Once a battery is in use, there are no further minerals necessary to sustain it. That’s a very different picture from oil and gas, which must constantly be drilled from the ground, transported via pipelines and tankers, refined and combusted in our gasoline cars to keep those cars moving, said Jim Krane, a researcher at Rice University’s Baker Institute for Public Policy in Houston. In terms of environmental and other impacts, he said, “There’s just no comparison.”

As E.V.s are to gas-powered cars, are there greener alternatives to fuel-powered planes that are close to commercialization? — Rashmi Sarnaik, Boston

There are alternatives to fossil-fuel-powered aircraft in development, but whether they are close to commercialization depends on how you define “close.” It’s probably fair to say that the day when a significant amount of air travel is on low- or zero-emissions planes is still far-off.

There has been some work on using hydrogen, including burning it in modified jet engines. Airbus and the engine manufacturer CFM International expect to begin flight testing a hydrogen-fueled engine by the middle of the decade.

As with cars, though, most of the focus in aviation has been on electric power and batteries. The main problem with batteries is how little energy they supply relative to their weight. In cars that’s less of an obstacle (they don’t have to get off the ground, after all) but in aviation, batteries severely limit the size of the plane and how far it can fly.

One of the biggest battery-powered planes to fly so far was a modified Cessna Grand Caravan, test-flown by two companies, Magnix and Aerotec. Turboprop Grand Caravans can carry 10 or more people up to 1,200 miles. The companies said theirs could fly four or five people 100 miles or less.

The limitations of batteries, at least for now, have led some companies to work on other designs. Some use fuel cells, which work like batteries but can continuously supply electricity using hydrogen or other fuel. Others use hybrid systems — like hybrid cars, combining batteries and fossil-fuel-powered engines. In one approach, the engines provide some power and also keep the batteries charged. In another, the engines are used in takeoff and descent, when more power is needed, and the batteries for cruising, which requires less power. That keeps the number of batteries, and the weight, down.

What countries, if any, have a realistic chance of meeting their Paris agreement pledges? — Michael Svetly, Philadelphia

According to Climate Action Tracker, a research group that analyzes climate goals and policies, very few. Ahead of United Nations talks in Glasgow last year, the organization found most major emitters of carbon dioxide, including the United States and China, are falling short of their pledge to stabilize global warming around 1.5 degrees Celsius, or 2.7 degrees Fahrenheit.

A few are doing better than most, including Costa Rica and the United Kingdom. Just one country was on track to meet its promises: Gambia, a small West African nation that has been bolstering its renewable energy use.

How is N.Y.C. planning for relocation or redevelopment, or both, of its many low-lying neighborhoods as floodwaters become too high to levee? — A reader in North Bergen, N.J.

New York City has yet to announce plans to fully relocate entire neighborhoods threatened by climate change, with all the steps that would entail: determining which homes to buy, getting agreement from homeowners, finding a new patch of land for the community, building new infrastructure, securing funding and so on.

Relocation projects on that scale, often described as “managed retreat,” remain extremely rare in the United States. What projects have been attempted so far have mostly been in rural areas or small towns, and their success has been mixed.

And the idea of pulling back from the water, while never easy, is especially fraught in New York City, which has some of the highest real estate values in the country. Those high values have been used to justify fantastically expensive projects to protect low-lying land in the city, rather than abandon it — like a $10 billion berm along the South Street Seaport, or a $119 billion sea wall in New York Harbor.

Perhaps unsurprisingly, then, the city’s most recent Comprehensive Waterfront Plan, issued in December, makes no mention of managed retreat. But the plan does include what it calls “housing mobility” — policies aimed at helping individual households move to safer areas, for example by giving people money to buy a new home on higher ground, as well as paying for moving and other costs. The city also says it is limiting the density of new development in high-risk areas.

Robert Freudenberg, a vice president of the Regional Plan Association, a nonprofit planning group in New York, New Jersey and Connecticut, gave city officials credit for beginning to talk about the idea that some areas can’t be protected forever.

“It’s an extremely challenging topic,” Mr. Freudenberg said. But as flooding gets worse, he added, “we can’t not talk about it.”

The oceans are predicted to rise and affect coastal areas and cities, however, does this rise also affect the coastal areas of the Great Lakes, as the lakes are connected to the Atlantic Ocean via the St. Lawrence River and one would have to assume they would eventually be impacted? — Terri Messinides, Madison, Wis.

The Great Lakes are not directly threatened by rising oceans because of their elevation: The lowest of them, Lake Ontario, is about 240 feet above sea level. The St. Lawrence River carries water from the lakes to the Atlantic Ocean, but because of the elevation change, rising waters in the Atlantic can’t travel in the other direction.

That said, climate change is causing increasingly frequent and intense storms in the Great Lakes region, and the effects, including higher water levels and more flooding, are in many respects the same as those caused by rising seas. It’s just a different manifestation of climate change.

When it comes to precipitation, the past five years, from April 2017 through March 2022, the last month for which complete data is available, have been the second-wettest on record for the Great Lakes Basin, according to records kept by the National Oceanic and Atmospheric Administration. The water has risen accordingly. In 2019, water levels in the lakes hit 100-year highs, causing severe flooding and shoreline erosion.

At the same time, higher temperatures increase the rate of evaporation, which can lead to abnormally low water levels. People who live around the Great Lakes can expect to see both extremes — high water driven by severe rainfall, and low water driven by evaporation — happen more often as the climate continues to warm.

Can you tell us about the damage being done to our environment by crypto mining? I’ve heard the mining companies are trying to switch to renewable energy, yet at the same time reopening old coal power plants to provide the huge amounts of electricity they need. — Barry Engelman, Santa Monica, Calif.

Cryptomining, the enigmatic way in which virtual cryptocurrencies like Bitcoin are created (and which is also behind technology like NFTs), requires a whole lot of computing power, is highly energy-intensive and generates outsize emissions. We delved into that process, and its environmental impact in this article — but suffice to say the problem isn’t going away soon.

The way Bitcoin is set up, using a process called “proof of work,” means that as interest in cryptocurrencies grows and more people start mining, more energy is required to mine a single Bitcoin. Researchers at Cambridge University estimate that mining Bitcoin uses more electricity than midsize countries like Norway. In New York, an influx of Bitcoin miners has led to the reopening of mothballed power plants.

But you might wonder about the traditional financial system: doesn’t that use energy, too? Yes, of course. But Bitcoin, for all its hype, still makes up just a few percent of all the world’s money or its transactions. So even though one industry study estimated that Bitcoin consumes about a 10th of the energy required by the traditional banking system, that still means Bitcoin’s energy use is outsize.

To address its high emissions footprint, cryptomining has increasingly tapped into renewable forms of energy, like hydroelectric power. But figuring out exactly just how much renewable energy Bitcoin miners use can be tricky. For one, we don’t exactly know where many of these miners are. We do know a lot of crypto miners used to be in China, where they had access to large amounts of hydro power. But now that they’ve largely been kicked out, cryptomining’s global climate impact has likely gotten worse.

In the United States, cryptominers have started to tap an unconventional new energy source: drilled gas, collected at oil and gas wells. The miners argue that this gas would otherwise have been flared or vented into the atmosphere, so no excess emissions are created. The reality is not that clear cut: If the presence of those cryptominers disincentivizes oil and gas companies from piping away that gas to be used elsewhere, any savings effect is blunted.

Other efforts are afoot to make cryptomining less damaging for the environment, including an alternative way of cryptomining involving a process called “proof of stake,” that doesn’t require miners to use as much energy. But unless Bitcoin, the most popular cryptocurrency, switches over, that’s going to do little to dent miners’ energy use.

What does the data look like for greenhouse gas emissions in the last 200 years if volcanic activity was subtracted out? — Haley Rowlands, Boston

Volcanic activity generates 130 million to 440 million tons of carbon dioxide per year, according to the United States Geological Survey. Human activity generates about 35 billion tons of carbon dioxide per year — 80 times as much as the high-end estimate for volcanic activity, and 270 times as much as the low-end estimate. And that’s carbon dioxide. Human activity also emits other greenhouse gases, like methane, in far greater quantities than volcanoes.

The largest volcanic eruption in the past century was the 1991 eruption of Mount Pinatubo in the Philippines; if an explosion that size happened every day, NASA has calculated, it would still release only half as much carbon dioxide as daily human activity does. The annual emissions from cement production alone, one small component of planet-warming human activity, are greater than the annual emissions from every volcano in the world.

There is also no evidence that volcanic activity has increased over the past 200 years. While there have been more documented eruptions, researchers at the Smithsonian Institution’s Global Volcanism Program found that this was attributable not to an actual trend, but rather to “increases in populations living near volcanoes to observe eruptions and improvements in communication technologies to report those eruptions.”

All told, volcanic activity accounts for less than 1 percent of greenhouse gas emissions, which is not enough to contribute in any meaningful way to the increase we’ve seen over the past 200 years. The Intergovernmental Panel on Climate Change found in 2013 (see Page 56 of its report) that the climatic effects of volcanic activity were “inconsequential” over the scale of a century.

Why is the concentration of carbon dioxide in the atmosphere at Mauna Loa Observatory in Hawaii used as the global reference? It’s only one point on Earth. Do concentrations vary between different parts of the world? — Evan, Boston

At any given moment, levels of carbon dioxide in the air vary from place to place, depending on the amount of vegetation and human activity nearby. Which is why, as a location to monitor the average state of the atmosphere, at least over a large part of the Northern Hemisphere, a barren volcano in the middle of the Pacific has much to offer. It’s high above the ground and far enough from major sources of industrial pollution but still relatively accessible to researchers.

Today, the National Oceanic and Atmospheric Administration studies global carbon dioxide levels by looking at readings from Mauna Loa Observatory and a variety of other sources. These include observatories in Alaska, American Samoa and the South Pole, tall towers across the United States, and samples collected by balloons, aircraft and volunteers around the world. (Here’s a map of all those sites.)

NOAA also checks its measurements at Mauna Loa against others from the same location, including ones taken independently, using different methods, by the Scripps Institution of Oceanography. On average, the difference in their monthly estimates is tiny.

Will increases in global temperature associated with climate change be mitigated by the coming of a new “ice age?” — Suzanne Smythe, Essex, Conn.

In a “mini ice age,” if it occurred, average worldwide temperatures would drop, thus offsetting the warming that has been caused by emissions of greenhouse gases from the burning of fossil fuels in the last century and a half.

It’s a nice thought: a natural phenomenon comes to our rescue. But it’s not happening, nor is it expected to.

The idea is linked to the natural variability in the amount of the sun’s energy that reaches Earth. The sun goes through regular cycles, lasting about 11 years, when activity swings from a minimum to a maximum. But there are also longer periods of reduced activity, called grand solar minimums. The last one began in the mid-17th century and lasted seven decades.

There is some debate among scientists whether we are entering a new grand minimum. But even if we are, and even if it lasted for a century, the reduction in the sun’s output would not have a significant effect on temperatures. NASA scientists, among others, have calculated that any cooling effect would be overwhelmed by the warming effect of all the greenhouse gases we have pumped, and continue to pump, into the atmosphere.

Genie Mathena

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