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One student asked me yesterday, " Can you explain why majority of scientists trust their colleagues when they say AGW is happening despite opposition from climate change deniers and their emotional arguments?"

My reply : Anthropogenic Global Warming or AGW, now accepted by majority of the scientists in the world,  suggests that increased CO2 concentration in the atmosphere, caused by humans, is raising global temperatures.

Respect for knowledge, evidence and reasoned argument is one of the important traits of people of science. At the same time they ignore cacophony based on emotions, misinformation, false assumptions and stupidity. Pure and simple!

That is why majority of scientists trust their colleagues in the field of climate science. Because scientists are in a position to understand and analyze data provided by the latter. Moreover, scientists belonging to various fields themselves are testing and providing data that indirectly proves that Earth is warming up because of man's activities.

Changes are occurring, according to collected data from around the world. Over the last 100 years, global temperatures have warmed by about 1.33 degrees Fahrenheit (0.74 degrees Celsius) on average. The change may seem minor, but it's happening very quickly — more than half of it since 1979 because of human activity.

Skeptics: How can you tell our Earth is actually warming and whether humans are to blame for it?

Scientists' reply: Climate changes have occurred ever since our planet came into existence. But what sets apart the present changes from those in the past is ...

Climate changes in the past suggest that our climate reacts to energy input and output, such that if the planet accumulates more heat than it gives off global temperatures will rise. It's the driver of this heat imbalance that differs. Currently, CO2 is imposing an energy imbalance due to the enhanced greenhouse effect. Past climate change actually provides evidence for our climate's sensitivity to CO2.

See below for understanding how human activity is responsible for this raise in temperatures.

Skeptics: But we are witnessing snow blizzards in several parts of the world, it is not a sign of global warming! Winters are becoming chilliest too!

SR: Local temperatures taken as individual data points have nothing to do with the long-term trend of global warming. These local ups and downs in weather and temperature can hide a slower-moving temperature raises in long-term climate. To get a real picture on global warming, scientists rely on changes in weather over a long period of time. To find climate trends you need to look at how weather is changing over a longer time span. Looking at high and low temperature data from recent decades shows that new record highs occur nearly twice as often as new record lows.

For instance, a study published in the journal Geophysical Research Letters in 2009, found that daily record high temperatures occurred twice as often as record lows over the prior decade across the continental United States (2).

This year the temperatures are the highest ever recorded and is a proof of temperature raises.

Globally coherent fingerprint of climate change impacts across natural systems are being studied systematically (5) by scientists. 

Skeptics: Sun's activity too causes temperature raises here on Earth. How can you say it really is AGW that  is responsible?

SR: According to scientists, in the last 35 years of global warming, the sun has shown a slight cooling trend, while the climate has been heating up! In the past century, solar activity can explain some of the increase in global temperatures, but a relatively small amount. (Solar activity refers to the activity of the sun's magnetic field and includes magnetic field-powered sunspots and solar flares.)

A study published in the journal Atmospheric Chemistry and Physics in December 2011 revealed that even during a prolonged lull in the sun's activity, Earth still continued to warm. The study researchers found that the Earth absorbed 0.58 watts of excess energy per square meter than escaped back into space during the study period from 2005 to 2010, a time when solar activity was low.

Skeptics: But plants need CO2 to prepare food for all of us!

SR: Right now we are producing more CO2 than plants can absorb. There is a surplus that is becoming a problem actually. While it is true that plants photosynthesize, and therefore take up carbon dioxide as a way of forming energy with the help of the sun and water, this gas is both a direct pollutant (think acidification of oceans) and more importantly is linked to the greenhouse effect. When heat energy gets released from Earth's surface, some of that radiation is trapped by greenhouse gases like CO2; the effect is what makes our planet comfortable temperature-wise, but too much of it get you to global warming.

Deforestation and land use change : Massive amounts of carbon are stored in tropical forests. When we destroy these areas to clear land for ranches or farms, that carbon gets released into the atmosphere and accelerates climate change. Studies show that deforestation accounts for 11% of all human-caused greenhouse gas emissions.

Skeptics: The scenery is not that bad!

SR: Climate scientists say any positives are far outweighed by the negative impacts of global warming on agriculture, human health, the economy and the environment. For instance, according to one 2007 study, a warming planet may mean an increased growing season in Greenland; but it also means water shortages, more frequent and more intense wildfires and expanding deserts. We are watching all these things before our eyes now!

Skeptics: Climate models are unreliable!

SR: Agreed some models were unable to paint a correct picture. 

"Models are simply a formalization of our best understanding of the processes that govern the atmosphere, the oceans, the ice sheets, etc." But don't forget that certain processes, such as how clouds will respond to changes in the atmosphere and the warming or cooling effect of clouds, are uncertain and different modeling groups make different assumptions about how to represent these processes.

Even so certain predictions are based on physics and chemistry that are so fundamental, such as the atmospheric greenhouse effect, that the resulting predictions — that surface temperatures should warm, ice should melt and sea level should rise — are robust no matter what the assumptions are.

Skeptics: Is there a consensus among scientists of various fields on this?

SR: About 97 percent of scientists agree that human-made global warming is happening. "In the scientific field of climate studies — which is informed by many other different disciplines — the consensus is demonstrated by the number of scientists who have stopped arguing about what is causing climate change — and that's nearly all of them," according to Skeptical Science, a website dedicated to explaining the science of global warming.

This consensus among the scientific community is based on the data and evidence provided by their colleagues in various fields.

Skeptics: Is there evidence that our planet is heating up more than necessary?

SR: Yes, there is! 

Receding glaciers, shown in satellite images. Islands disappearing or becoming small. Changes are degrading and destroying wetlands and coastal forests — the natural buffers that help protect coastal areas against storm surges, rising sea levels and erosion.

Ecological responses to climate changes are clearly visible (6).

The indirect evidence ... according to scientists working in several fields (4,1) ... 

1. Vegetables getting bitter (3), flowers loosing scent (4) and these are undoubtedly climate change evidences. Climate even effects human behaviour according to recent studies  (7).

2. The people and  military of various countries around Arctic are moving more to north ... as the Arctic ice opens up, the world turns its attention to the resources below. 30 percent of the world's undiscovered natural gas and 13 percent of its undiscovered oil are under this region. As a result, military action in the Arctic is heating up, with the United States, Russia, Denmark, Finland, Norway, Iceland, Sweden and Canada holding talks about regional security and border issues. Several nations, including the U.S., are also drilling troops in the far north, preparing for increased border patrol and disaster response efforts in a busier Arctic.

3. Breeding season alterations among animals ... 

As temperatures shift, penguins are shifting their breeding seasons, too. A March 2012 study found that gentoo penguins are adapting more quickly to warmer weather, because they aren't as dependent on sea ice for breeding as other species.

It's not just penguins that seem to be responding to climate change. Animal shelters in the U.S. have reported increasing numbers of stray cats and kittens attributed to a longer breeding season for the felines.

4. High-country changes ...

Decreased winter snowfall on mountaintops is allowing elk in northern Arizona to forage at higher elevations all winter, contributing to a decline in seasonal plants. Elk have ravaged trees such as maples and aspens, which in turn has led to a decline in songbirds that rely on these trees for habitat.

5. Spring has changed in the last century (4)...

Spring is emerging progressively earlier than previous times since 1960s. This has set in noticeable changes in plants. Compared to the late 1800s, the first flowering dates for 43 of the most common plant species in the area have moved forward an average of 10 days. Other plants have simply disappeared, including 15 species of orchids.

6. Changed high season at parks ...

Peak national park attendance has shifted forward more than four days, on average, since 1979. Today, the highest number of visitors now swarm the Grand Canyon on June 24, compared with July 4 in 1979.

7. Changing genetics...

Even fruit flies are feeling the heat. According to a 2006 study, fruit fly genetic patterns normally seen at hot latitudes are showing up more frequently at higher latitudes. According to the research, the gene patterns of Drosophila subobscura, a common fruit fly, are changing so that populations look about one degree closer in latitude to the equator than they actually are. In other words, genotypes are shifting so that a fly in the Northern Hemisphere has a genome that looks more like a fly 75 to 100 miles (120 to 161 kilometers) south.

8. As space increases because of ice-melting, polar bears are swimming long distances ...

Polar bear cubs are struggling to swim increasingly long distances in search of stable sea ice, according to a 2011 study. The rapid loss of sea ice in the Arctic is forcing bears to sometimes swim up to more than 12 days at a time, the research found. Cubs of adult bears that had to swim more than 30 miles (48 kilometers) had a 45 percent mortality rate, compared with 18 percent for cubs that had to swim shorter distances.

9. Mobility of more species ...

Species are straying from their native habitats at an unprecedented rate: 11 miles (17.6 km) toward the poles per decade. Areas where temperature is increasing the most show the most straying by native organisms. The Cetti's warbler, for example, has moved north over the last two decades by more than 90 miles (150 km).

When there is so much evidence  - both direct and indirect -  from almost all the areas of science to show that climate change has entered our homeland and is about to stay and impact us in numerous negative ways unless we make adjustments to our lifestyles drastically, how can anybody with reasonable reasoning deny it?   

10. Altering interactions among Species (8)...

From plants and crustaceans to birds and mammals, species across the food chain in the world are shifting how they respond to seasonal changes, and British researchers say climate change is a major reason why.

Not all species were responding to environmental changes in the same way. The predatory species at the top of the food chain were changing the timing of their seasonal activities more slowly in response to warmer temperatures than other organisms. This suggests that species lower down on the food chain will change their behavior more as temperatures continue to rise.

Fish and insects modify seasonal habits more than plankton and birds, potentially pulling apart food webs and causing major damage to ecology, according to scientists. 

11. Decreasing economic productivity around the world (9, 10, 11)...

 In a sweeping new study published  in Nature, a team of researchers say there is a strong relationship between a region’s average temperature and its economic productivity — adding another potential cost to a warming climate.

From construction workers in Dubai to farmers in India, workers around the world are suffering from excessive heat fueled by climate change. This heat is leading to huge productivity losses and mounting economic strain for dozens of countries, according to research published on 18th July, 2016, ahead of a U.N. forum. The study builds on research detailing how extreme heat in some places prevents employees from working during the hottest hours of the day. People simply tire faster and accomplish less the hotter it gets. That lost work time translates into significant hits on the gross domestic product in nations across the globe, and it is a problem that could deepen as the Earth continues to warm.

Kjellstrom and fellow researchers found that in dozens of countries, daylight work hours lost to excessive heat have increased since the 1990s. They also estimate that at the current rate of global warming, that trend will continue. For instance, countries such as India, Vietnam and Indonesia could see the number of lost work hours more than double by 2055 and more than triple by 2085. By the mid-1990s, persistently hot, poor countries such as Bangladesh were estimated to have lost 1 to 3 percent of all daylight work hours to extreme heat, which can cause exhaustion, stroke and sometimes death among exposed workers. In West Africa, research found that the number of very hot days per year had doubled since 1960. Serious heat waves have become more prevalent in various parts of the globe. Those figures could only be getting worse over time.

The effects of heat stress aren’t felt only at the country level, but also at the human level.

Not only does extreme heat put the health of individual workers in danger, but it also hurts workers and their families financially.

References:

1. http://www.livescience.com/23026-global-warming-changing-world.html

2. http://www.livescience.com/5855-record-highs-outpace-record-lows.html

3. http://kkartlab.in/group/some-science/forum/topics/why-do-some-frui...

4. https://books.google.co.in/books?id=0FO3BgAAQBAJ&pg=PA223&l...

5. http://www.nature.com/nature/journal/v421/n6918/full/nature01286.html

6. http://www.nature.com/nature/journal/v416/n6879/full/416389a.html

7. http://www.sciencecodex.com/how_does_climate_affect_violence_resear...

8. http://www.nature.com/nature/journal/vaop/ncurrent/full/nature18608...

9. http://www.pnas.org/content/107/35/15367.full

10. http://www.nber.org/papers/w20750

11. http://www.nature.com/nature/journal/v527/n7577/full/nature15725.html

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Replies to This Discussion

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City Lights Trick Trees into an Earlier Spring

The Earth's temperature is rising. And as it does, springtime phenomena—like the first bloom of flowers—are getting earlier and earlier. But rising temperatures aren't the only factor. Urban light pollution is also quickening the coming of spring. "So temperature and light are really contributing to a double whammy of making everything earlier." Richard ffrench-Constant, an entomologist at the University of Exeter.

He and his colleagues compiled 13 years of data from citizen scientists in the U.K., who tracked the first bud burst of four common trees. Turns out, light pollution—from streetlights in cities, and along roads—pushed bud burst a full week earlier. Way beyond what rising temperatures could achieve. This disruptive timing can ripple through the ecosystem. 

"The caterpillars that feed on trees are trying to match the hatching of their eggs to the timing of bud burst. Because the caterpillars want to feed on the juiciest and least chemically protected leaves. And it's not just the caterpillars, of course, that are important. But the knock-on effect is on nesting birds, which are also trying to hatch their chicks at the same time that there's the maximum number of caterpillars." So earlier buds could ultimately affect the survival of birds, and beyond. The findings are in the Proceedings of the Royal Society B. [Richard H. ffrench-Constant et al., Light pollution is associated with earlier tree budburst across the...]

The world's becoming increasingly urbanized, and light pollution is growing—which ffrench-Constant says could trick trees into budding earlier and earlier. But smarter lighting—like LEDs that dial down certain wavelengths—could help. "Perhaps the exciting thing is, if we understand more about how light affects this bud burst, we might be able to devise smarter sort of street lighting that has less red components, and therefore less early bud burst." Thus keeping springtime an actual springtimephenomenon.

http://www.scientificamerican.com/podcast/episode/city-lights-trick...

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A graduate student at The University of Toledo recently won an award from the Ecological Society of America for his study that shows why the combination of high carbon dioxide levels in the air and chronic global warming will contribute to a decrease in crop production and food quality during the next few decades.

“We have provided a better understanding of what scientists need to do to improve the heat tolerance of crops in the future,” said Dileepa Jayawardena, a PhD student in the Department of Environmental Sciences who conducted the climate change study as a project for his master’s degree. “They can use this information to generate new climate-change-tolerant crops to help feed the growing human population.”

Tomatoes in growth chamberUsing tomato as a model, Jayawardena investigated the way plants absorb nitrogen fertilizer from the soil.

Over the course of 18 days inside controlled growth chambers at Bowman-Oddy Laboratories, Jayawardena’s team subjected the plants to conditions that mimic future climate.

Individually, elevated carbon dioxide and warming did not have large effects on tomato responses.

However, when combined, researchers saw a large decrease in the uptake rate of soil nitrate and ammonium through the roots. At the same time, researchers saw a significant drop in the concentration and function of the proteins that roots use to acquire soil nitrogen. The result was a crop with lower nitrogen levels and thus lower nutritional value.

Jayawardena’s work also shows that the combination of heat and carbon dioxide is bad for the plant in terms of being able to convert inorganic nitrogen, like nitrate and ammonium, into organic form, like protein, which is the form of nitrogen that humans require.

“If climate change intensifies, this impact on plant nitrogen concentration means that plants will not grow as big in the future, and they will be poorer-quality food for people and other animals that eat plants,” Jayawardena said.

Jayawardena won the New Phytologist Poster Award for his presentation at the Ecological Society of America annual meeting last month in Florida. It is the nation’s largest organization of professional ecologists with a membership of more than 10,000 scientists.

“By itself, increases in atmospheric carbon dioxide levels tend to increase plant growth, which is a positive,” said Scott Heckathorn, UT ecology professor and Jayawardena’s faculty advisor. “However, increasing carbon dioxide is the primary cause of current global warming, which will increase heat stress for much life on the planet. The question then arises as to whether benefits of elevated carbon dioxide will offset the negative effects of increasing heat stress. What is new about Dileepa’s work is that it provides a mechanism for why the combination of elevated carbon dioxide and heat is detrimental.”

The research was funded by the U.S. Department of Agriculture.

http://media.utoledo.edu/2016/09/07/ut-grad-student-honored-for-ide...

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https://www.theguardian.com/environment/2013/apr/13/climate-change-...

How do we know humans are causing climate change? By conducting research and finding evidence

The research falls into nine independently studied, but physically related, lines of evidence (12):

  1. Simple chemistry – When we burn carbon-based materials, carbon dioxide (CO2) is emitted (research beginning in the 1900s).
  2. Basic accounting of what we burn, and therefore how much CO2 we emit (data collection beginning in the 1970s).
  3. Measuring CO2 and other greenhouse gases in the atmosphere and trapped in ice to find they are increasing, with levels higher than anything we've seen in nearly a million years (measurements beginning in the 1950s).
  4. Chemical analysis of the atmospheric CO2 that reveals the increase is coming from burning fossil fuels (research beginning in the 1950s).
  5. Basic physics that shows us that CO2 absorbs heat (research beginning in the 1820s).
  6. Monitoring climate conditions to find that the air, sea and land is warming, as we would expect with rising greenhouse gas emissions; as a response, ice is melting and sea level is rising (research beginning in the 1930s).
  7. Ruling out natural factors that can influence climate like the sun and ocean cycles (research beginning in the 1830s).
  8. Employing computer models to run experiments of natural versus human-influenced simulations of Earth (research beginning in the 1960s).
  9. Consensus among scientists who consider all previous lines of evidence and make their own conclusions (polling beginning in the 1990s).

Footnotes: https://www.edf.org/climate/9-ways-we-know-humans-triggered-climate...

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  • We know that carbon dioxide (and other greenhouse gases) trap heat in the Earth’s atmosphere.
  • And we know that humans are burning fossil fuels, releasing huge amounts of carbon pollution and trapping more and more heat in the atmosphere.
  • There’s only one conclusion: humans are the primary reason we see our climate changing today.

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