Can you explain global warming to me ?
I'm very confused about global warming. People always tell me how urgently we need to respond to global warming and they make it seem like temperatures have been rising exponentially. So I decided to research global warming and decide for myself if this is the case ( I have just been taking people's word for it before this). I found out that the earth has warmed up 1.3 degrees over the past 100 years. THAT is what people are so concerned about? The temperature must have risen a lot more than that in order for the ice age to end! Also, I can't seem to find anything about temperatures before the 20th century so how do we know that we're in trouble? (Or maybe I just couldn't find the data). Actually, we had a colder than usual winter where I live this year and some of my friends suggest that that's because of global warming. But then why is it called global WARMING? Changing temperatures just seem normal to me. And if it only rises about 1 degree each century then shouldn't everyone just calm down a bit and be confident that American ingenuity will solve the problem if there is one? So as you can see, the global warming issue confuses me. I could be wrong as I clearly do not know a lot about it but generally it just does not seem to make sense. Thanks in advance for answering and giving your opinion.
● Can you explain global warming to me?
Dawei, Antarcticice and MTRstudent have each provided you with excellent answers (they each have relevant qualifications so know a lot about climate change). I’ll add my contribution by taking each of your points in turn…
● I'm very confused about global warming.
There are a lot of conflicting arguments out there and this is causing a lot of confusion for many people. Effectively you have the scientists on one side claiming that global warming is real and on the other side you have groups funded by the oil and power industries claiming it’s not real.
● People always tell me how urgently we need to respond to global warming
The effects of global warming are progressive. There will be no sudden overnight changes and no scenarios as depicted in the movies. The longer we leave it the harder and more expensive it becomes to deal with. The damage that global warming causes increases each year, so too does the number of people, plants and animals that are dying or being adversely affected.
● and they make it seem like temperatures have been rising exponentially.
Temperatures are rising faster now than has ever before been known, the rise isn’t exponential but it’s very significant (more later).
● So I decided to research global warming and decide for myself if this is the case ( I have just been taking people's word for it before this).
Always a good idea to conduct your own research. But a word of warming, do check the validity of your sources. Much of what you read in the media is written by journalists who have little or no understanding of the science involved, make sure they cite their sources and that these sources are reliable. Ignore journals, blogs, forums etc as these can be written by anyone at all, they are often very biased and in the worst cases they invent whatever ‘evidence’ is needed to validate their argument.
● I found out that the earth has warmed up 1.3 degrees over the past 100 years.
In 1910 the average global temperature was between 13.588°C (56.458°F) and 13.702°C (56.664°F). Today it is between 14.475°C (58.055°F) and 14.542°C (58.176°F). The difference being between 0.773°C (1.391°F) and 0.954°C (1.717°F). The actual figures vary depending on the source and method used to calculate the temperature.
● THAT is what people are so concerned about?
It doesn’t seem much of a rise does it. However, it needs to be put into context. In terms of Earth’s natural variability and adaptability this far exceeds normal parameters. Temperatures are rising and the climate is changing much faster than our planet and many of the species upon it can adapt to.
● The temperature must have risen a lot more than that in order for the ice age to end!
Yes it did. But again, it’s a matter of context. The last ice-age began to end some 19,000 years ago at which time the average global temperature was 8°C (14°F) colder than it is today. For 12,000 years the ice melted as the world warmed up. By the end of the ice-age temperatures had increased by 7°C (13°F).
This 7°C (13°F) rise took place over 12,000 years. That’s the equivalent of 1°C (1.8°F) every 1700 years. In today’s world we’re seeing that same level of increase every 54 years, more than 30 times as fast as during the ending of the ice age.
● Also, I can't seem to find anything about temperatures before the 20th century so how do we know that we're in trouble? (Or maybe I just couldn't find the data).
It looks like the data eluded you. The earliest instrumental (thermometer) record dates from 1659, this is a record known as HadCET, the most comprehensive record runs from 1850 and this is known as HadCRUT3. Both these, any dozens of others, can be viewed and downloaded from the UK’s Met Office http://hadobs.metoffice.com/index.html
When we go back further in time we need to use a different technique, it becomes necessary to reconstruct temperature data. There are many ways of doing this but one of the most accurate and extensive methods is through oxygen isotope analysis.
In the polar regions and mountainous regions the snow never melts, it simply accumulates layer upon layer and compresses into ice. Trapped within the ice are bubbles of air from the time the snow fell. We can take cores from the ice, melt the ice in hermetically sealed (airtight) chambers and analyse the air. In particular we’re looking at the different types of oxygen and deuterium. Oxygen for example, comes in different forms (isotopes) and the relationship between these forms is extremely sensitive to temperature. The ratio of oxygen isotope 16 to isotope 18 enables us to determine just what the temperature was right back for almost a million years.
Here’s more about the sampling techniques http://en.wikipedia.org/wiki/Ice_core and graphs showing temps over the last 12,000 years http://commons.wikimedia.org/wiki/File:Holocene_Temperature_Variations.png the last 450,000 years http://commons.wikimedia.org/wiki/File:Ice_Age_Temperature.png and the last 5.5 million years http://commons.wikimedia.org/wiki/File:Five_Myr_Climate_Change.png
● Actually, we had a colder than usual winter where I live this year and some of my friends suggest that that's because of global warming. But then why is it called global WARMING?
The cold weather that affected parts of the US and Europe this last winter was caused by a cyclical weather event. At intervals of approx 15 years, changes in atmospheric and oceanic conditions in the North Atlantic region lead to an area of high pressure establishing itself over the Arctic, this feeds cold air into parts of the surrounding northern hemisphere.
When you look back at previously harsh winters you’ll notice a regular pattern – 1917, 1931, 1946, 1963, 1979, 1995 and now 2009. It’s likely we’ll see the next similar event in about 2024. Of the 15 instances on record, the most recent one was actually the mildest.
● Changing temperatures just seem normal to me.
Throughout the history of Earth, the temperatures have always changed. There have been instances when it’s been so warm that the North and South Poles have had tropical climates, similarly there have been times when it’s been cold enough to freeze the whole planet. Changes of this magnitude happen extremely slowly, over many millions of years.
Natural changes are determined by numerous cycles, mostly relating to the behaviour of the Sun and / or the way that Earth moves in space. These changes happen very slowly, not even close to the current rate of change.
● And if it only rises about 1 degree each century then shouldn't everyone just calm down a bit and be confident that American ingenuity will solve the problem if there is one?
It’s a matter of keeping it in context. Climate change will not be as extreme as some people claim but we are already seeing noticeable effects including a doubling in the number of category 5 hurricanes, millions of square kilometres of ice and permafrost having melted, millions forced from their homes due to encroaching deserts and rising sea levels, the spread of tropical diseases etc.
The Americans are behind much of the world when it comes to using ingenuity to solve the problem. There are about 20 different scientific and technological solutions that have been proposed, most of them have come from Europe.
● So as you can see, the global warming issue confuses me. I could be wrong as I clearly do not know a lot about it but generally it just does not seem to make sense.
The climate is phenomenally complicated, it’s necessary to have quite a bit of background information before it starts to make sense and the pieces fit together. It is not something that can be learned from the media, friends, internet blogs etc. There are about a dozen people here on Answers that sufficiently understand the mechanisms involved, most of these people have degrees and doctorates in relevant subjects.
● Thanks in advance for answering and giving your opinion.
You’re welcome. I know there’s a lot of points that I mentioned, please feel free to ask if you want clarification or more details about any of these issues.
The 1.3 F rise that we have seen so far is not what people are concerned about. It (obviously) has not caused too much destruction so far. It is the potential of a future, significant warming that people are concerned about, of something like 3 or 4 C by the end of the century.
The difference between an ice age climate and that of an interglacial (which is what we are in today) is only about 5 or 6 C.
It doesn't sound like a huge difference, but it is enough to completely change the climate. An ice age Earth looks completely different from an interglacial one.
As you can see from the above, we do have somewhat reliable ways of figuring out how temperatures have changed even though we don't have direct instrument measurements. This is done through using proxies, such as tree rings or studying the ratio of oxygen isotopes trapped in air bubbles from ice cores. Using several different, independent proxies and comparing their results is a good way to have confidence in their accuracy, as you can see here:
Your friends are wrong. It always happens that some places feel colder than usual or hotter than usual. The climate is complicated, but all it really takes to have a colder than usual winter is for a cold air mass to roll down to wherever you are from the North. Even though this winter was very cold for some places, globally it was still the warmest Jan-Feb-March ever recorded.
April 2010 was the warmest April ever recorded. Yet many places were still quite chilly compared to what they usually are, such as much of China, Japan, and Korea. This is true every month. http://goo.gl/L2Gck
A warning for all: don't waste your bandwidth on Harvs link it has noting to do with the subject from either side and is pure trolling. If trolls have to post this rubbish they could at least use someone who can actually sing. Back to the question
You don't supply a link or mention who said temperatures were going up 'exponentially' so it's hard to make a comment on such unsupported statements.
As far as temperature goes 1.3 deg as a global average rise in just a century is a quite a marked rise given that the average temperature only has to rise about 8 deg for the planet to be ice free. The 1.3 is and average the rate of warming in the Arctic is almost twice this rate, which is why this is happening.
Just a few weeks ago deniers were crowing that the Arctic had returned to normal (after a cold Northern Winter) it was explained to them that this was a short term event and would melt quickly as Summer returned, which is exactly what happened and now they have gone very quite on the subject.
As far as it only rising 1deg a century that is not the likely case if the science is correct and our GH gas emissions are to blame those emissions are going up at an 'exponential rate' (this time the use of the word is correct) if we act and reduce our current emissions by changing technologies for transport and energy we may hold the temperature increase to 2 deg if we don't then we face the likelihood of rises of more like 3-5 deg which would have marked affects on both global weather systems and sea level rise.
We know from historical tidal records that historic sea level rise was (over the last century was ~1.7mm per year and that rate almost doubled in the early 1990's
Deniers will tell you that sea level has been rising since the end of the last ice age and it is certainly true that levels did rise significantly, as can be seen here
but this slowed significantly ~7000 years ago and more or less stopped ~2000 years ago. If seas had been rising, using the smaller (1.7mm) figure, for the last 2000 years sea levels would have risen 3.4m, they didn't. Which on the graph above would be a line at near 45degs line instead of the flat line shown.
Dawei and antarcticice covered it well!
A few other bits: we can estimate temperature from thousands of years ago by doing things like counting the ratio between different isotopes of oxygen in ice cores AND in sediment cores (bit of rock dug up from the floor of the ocean, made from shells etc all squashed together). In sediment cores they can count the different types of foraminifera, little critters with shells that either curl left or right; one type dominates in cold water, the other in warm water.
Anyway, people tested both and came up with a history; they put them side by side and they matched, so they're probably quite reliable.
(bottom shows 'benthic forams,' those little critters from sediment cores, vs ice cores using oxygen isotope data). An ice age appears to be about 4-6C cooler than today.
Every doubling of CO2 is believed to cause 2-4.5C of warming, with a best estimate of 3C:
and if we didn't do anything, we'd probs do TWO doublings, i.e. 6C of _global_ warming: more than the difference between today and Scotland being covered in ice.
The warming is sort of going exponentially: we expect temperature rise to continue accelerating, but it will seem very slow to begin with. We raised temperatures 0.17C from the '90s to the '00s. We expect this to slowly increase, but you'll still probably only see ~0.02C rise temperature a year for a couple of decades yet. The solar cycle causes ~0.1C of cooling or warming in about 5 years, and El Nino can cause 0.4C of change in months. This makes it very hard to pick out if you look at very short trends (less than a decade, or maybe even 2):
on top of that, you have the confusion between weather and climate. It's been chilly in N Europe and the USA over the winter, but Canada, the Pacific, S America, S Atlantic, Australia, India, Middle East, Africa, Indian Ocean, Tibet and SE Asia were all warm.