What is climate? | Quaternary climates | Is our climate changing? | The Role of Carbon Dioxide | Climate change in Antarctica | Observed impacts of climate change | References | Comments |
What is climate?
First, it is important here to note the differences between weather and climate. Weather is local and what you can see out of your window; weather is the cold British winter snows in 2011 and our 2012 wet and rainy summer (these are to do with short term variations in winds and atmospheric pressures), or heat waves in the USA in July 2012.
Climate is much broader scale; we are looking at long term statistical patterns in weather. An individual flood or storm is not caused by climate change, but climate change may make extreme weather events (like floods) occur more frequently. “Climate” encompasses data such as temperature, humidity, pressure, wind, precipitation (snow or rain), and other meteorological measurements.
This page is intended to be a short introduction, and by no means covers all of the vast topic of climate change. For more information, see: New Scientist; IPCC; Met Office.
Quaternary Climates
Throughout the last 2.6 million years (the “Quaternary Period”), the earth’s climate has oscillated many times, swinging between glacial and interglacial states (Figure 1). Over the last ~1 million years, we have experienced large ice ages and interglacials with a periodicity of around 100,000 years.
We are currently in an interglacial state, which began at the start of the Holocene, ~11,500 years ago. About 104 stages of these cold and temperate cycles have been recognised in deep ocean marine sediment cores (Figure 1) (Lowe and Walker, 1997). During glacials, large ice sheets developed in mid- to high-latitudes, including over Britain and North America.
Repeated climate oscillations
These large changes are driven by changes in the earth’s orbit around the sun – see The Quaternary Period (Table 1) (Jouzel et al., 2007). Glacials and interglacials can be further divided into stadials and interstadials, and within these we have smaller scale Dansgaard-Oeschger cycles, and then even smaller cycles, such as El-Nino and ENSO.
Climate data is therefore very noisy, and climate scientists must determine patterns in this data using complex statistical techniques. Throughout this time, carbon dioxide has mirrored temperature variations, which have formed a regular pattern.
Climate variations are a natural part of the earth system. It is therefore important, using instrumental records and proxies (such as ice cores, or microfossils in marine sediment cores), to compare current trends with those in the past (Bentley, 2010).
Is our climate changing?
Recent Change
The Earth warmed by an average of 0.6 ± 0.2°C during the twentieth century (Houghton et al., 2001). Rapid warming has been measured with global instrumental data since the 1800s (Figure 2). In 2019, the global average temperature was 0.95°C above the twentieth Century average, making it the second warmest year on record. The five warmest years have all occurred since 2015, and nine of the 10 warmest years since 2010 (Climate.Gov, accessed August 19, 2020).
The 2001 IPCC report stated that most of this warming was likely to have been due to an increase in greenhouse gas emissions. Later IPCC reports have stated this with ever increasing confidence. However, this average rate hides considerable variations in the rate and magnitude of warming.
Regional Rapid Warming
Climate change varies seasonally, on decadal timescales, and is geographically patchy (Mann et al., 2008). Three areas in particular have been subject to recent regional rapid warming (sensu Vaughan et al., 2003), with rates of warming far faster than the average noted in the IPCC. These regions are: north-western North America, the Siberian Plateau in northeast Asia, and the Antarctic Peninsula and Bellingshausen Sea. These areas warmed by more than 1.5°C between 1950 and 2000 AD (compared with a global mean of 0.5°C) (Mann et al., 2008).
More populated regions have atmospheric sulphate aerosols, that may mask warming. Urban meteorological stations may also record anomalous warming due to urban heat island effects. However, the Antarctic continent is free of these effects. Although direct meteorological observations are short (~60 years), trends in these areas are particularly important.
The Longer Term View
Although we have measured changing temperatures and carbon dioxide levels at short timescales (since the 1700s), surely this could just reflect natural variability over short timescales? In order to understand our climate, it is very important to look at the long-term view.
In many places, atmospheric temperatures are now warmer than they have been throughout the Holocene. Figure 3 shows that the temperature of the last 200 years is much higher than it was when Romans were making wine in southern England. However, what is really concerning is the rate of change. Temperatures have risen far more sharply in the last century than they have at any point in the last 2000 years.
This conclusion is reached again and again, and a paper by Mann et al. (2008) in PNAS show that the Earth’s temperature is anomalous in a long-term time context. Mann et al. used stacked records from a variety of sources to create a global graph of temperature change. This famous ‘hockey stick’ graph (Figure 4) clearly demonstrates the rapid rate of change since the industrial revolution, with temperature rise sharply accelerating over the last 150 years.
The Pages2k team have compiled global temperature records over the last 2000 years (Pages 2k Team, Nature Geoscience 12, 643-649). This reconstruction comes from many different kinds of proxy records, including tree rings, cave deposits, corals, etc.
Ed Hawkins (website: Climate Lab Book) has visualised the Pages2k climate record for the years 0 AD to 2019 AD using #warmingstripes (Figure 5). The colours highlight the recent very rapid warming.
The uncertainty estimates mean that you can also view the dataset in a more traditional way. The Medieval Warm Period and Little Ice Age are clearly shown, and the highly unusual recent rapid warming. The Medieval Warm Period and Little Ice Age are relatively small phenomena compared with the recent rapid warming.
Climate change over the last 11,300 years
A paper out in Science by Marcott et al. (2013) extends Figures 3 and 4 back to the last 11,300 years, with the Earth’s temperatures now warmer than the Earth was 4000 years ago (Figure 7). During the last 200 years, temperatures have rocketed up, confirming earlier reconstructions by Mann et al. 2008.
Although the Earth has not yet exceeded the temperatures of the Early Holocene (5000 to 11,000 years ago), global temperatures have risen from cooler than 95% of the Holocene at around 1900 to warmer than 72% of the Holocene in the last 100 years (Figure 7).
This means that, in the last 100 years, the Earth’s temperature has reversed a long-term cooling trend that began around 5000 years ago to become near the warmest temperatures during the last 11,000 years. Furthermore, climate models predict that the Earth’s temperature will exceed the warmest temperatures of the Holocene by 2100, regardless of which greenhouse gas emission scenario is used (Marcott et al., 2013).
However, Marcott et al. do note in their paper that the ‘uptick’ shown in the graph is not statistically robust, as the median resolution of all data is 120 years. However, this has been shown by other authors, such as Anderson et al. 2013, who demonstrate rapid warming over the last century from geological data.
Kaufman et al. (2020) provide an updated global temperature reconstruction, dating back to 12,000 years ago (Figure 8). They used a median from five different reconstruction methods, generating a consensus global mean surface temperature reconstruction. It follows the same approach as the PAGES 2k Consortium.
Kaufman et al. (2020) found that the warmest period in the Holocene was centred at 6,500 years ago, and was 0.6°C warmer than the 1800-1900 reference period.
The decade of 2011-2019 averaged 1 °C higher than 1850–1900 (Kaufman et al., 2020). For 80% of the ensemble members, no 200 year interval in the last 12,000 years was warmer than the last decade. Temperatures projected in the rest of this century, and beyond, are very likely to exceed 1 °C above pre-industrial temperature (IPCC, 2013).
The temperatures reconstructed vary in the different latitudes and different hemispheres; the palaeoclimate of the Northern and Southern hemispheres is very different (Figure 9).
Below, you can see the Kaufman et al. 2020 reconstruction, compared with other published proxy reconstructions over this time period. There are more proxy datasets from the Northern Hemisphere than the Southern Hemisphere.
Going back to the Last Glacial Maximum
However, it doesn’t end there. Using more proxies to extend the temperature graph back to the last glacial and modelling scenarios from the IPCC for the next 100 years, the graph below (Figure 11) has been created. Dubbed “The Wheelchair”, it shows the current and future alarming rate of temperature increase, compared with temperature fluctuations over the last 20,000 years. This figure was created by Jos Hagelaars.
The role of carbon dioxide
Carbon dioxide is a key factor in climate change. Carbon dioxide concentrations fluctuate annually, as seen in Figure 12 from the longest direct measurements of CO2 from Mauna Loa in Hawaii.
You can explore the changing global levels of carbon dioxide, methane, the global temperature record over the last 2000 years and global mean sea level here.
This article from Bloomberg allows you to investigate the factors that may cause global temperature variations, including solar changes, volcanism, aerosols, deforestation, and carbon dioxide.
The seasonal fluctuation is caused by variations in uptake of carbon dioxide by land plants. However, looking at Figure 2 above, you can see that this is just part of a much longer record of carbon dioxide. The IPCC 2007 Synthesis Report stated:
“Global GHG emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004”.
IPCC 2007
These increases in carbon dioxide are primarily due to increased use of fossil fuels, but land use changes also provide a significant contribution. You can explore global energy production at the Global Electricity Review website.
Because humans are constantly adding more carbon dioxide to the atmosphere, we are changing its balance and affecting the Earth’s climate. The carbon dioxide and other atmospheric gasses in the atmosphere combine with changes in land cover and solar radiation to drive climate change. They affect the absorption, scattering and emission of radiation within the Earth’s atmosphere, resulting in a positive energy balance and warming influences on our climate.
The IPCC 2007 states that there is very high confidence that the world has warmed since 1750, and that the combined radiative forcing due to increases in carbon dioxide, methane and nitrous oxide is 2.3W/m2, and that the rate of increase during the industrial era is was unprecedented in the last 10,000 years.
Changes in solar irradiance since 1750 AD have caused a small radiative forcing of +0.12 W/m2.
But how has carbon dioxide changed over the last few thousand years?
Figure 14 shows the long-term temperature and carbon dioxide record from Antarctica. Carbon Dioxide (blue line) now approaches 400 parts per million, which is far higher than it has been at any point in the last 400,000 years.
Methane (green line) is also higher than it has been before over this timescale. You can also see how closely temperature (red line) has tracked carbon dioxide and methane over this time. The temperature in Antarctica (red line) is expected to continue to rise with this increase in atmospheric greenhouse gases.
Climate change in Antarctica
The western Antarctic Peninsula warmed by 2.5°C from 1950-2000 (Turner et al., 2005) (Figure 15). The mean annual temperature is rising, with the -9°C isotherm moving southwards, resulting in the collapse of several ice shelves (28,000 km (Turner et al., 2005) of ice shelf has been lost since the 1990s) (Morris and Vaughan, 2003). Climate records from the South Orkney islands suggest that warming began in earnest in the 1930s (Mann et al., 2008).
Southern Westerly Winds
This warming has been related to variations in the belts of upper atmosphere winds that encircle the Antarctic continent (the Circumpolar Vortex) (Figure 16).
Periodic oscillations in this result in the periodic strengthening and weakening of this belt of winds. A strengthening of this vortex has been associated with changes in surface atmospheric pressures (van den Broeke et al., 2004). This pressure pattern causes northerly flow anomalies, which in turn cause cooling over East Antarctica and warming over the Antarctic Peninsula.
Other factors contributing to the recent regional rapid warming over the Antarctic Peninsula include decreased sea ice in the Bellingshausen Sea, resulting in warmer air temperatures, and decreasing precipitation over the south western peninsula (van den Broeke and van Lipzig, 2004; van Lipzig et al 2004).
Finally, since the 1950s, the Antarctic Circumpolar Current has warmed by +0.2°C, with the warming greatest near the surface (Gille, 2008). Waters west of the Antarctic Peninsula have also warmed rapidly (Turner et al., 2005; Mayewski et al. 2009).
This video from NASA shows global warming since 1884, and you can really see the large and rapid warming around the Antarctic Peninsula over the last 50 years.
Observed impacts of climate change
The impacts of this recent regional rapid warming around the Antarctic Peninsula have been dramatic, with the collapse of ice shelves (Cook and Vaughan, 2010), and with 87% of glaciers in recession (Cook et al. 2005). The present-day ice loss from the Antarctic Peninsula is -41.5 giga-tonnes per year (Ivins et al. 2011). Ice-shelf tributary glaciers have become destabilised following ice-shelf collapse (Scambos et al. 2004; DeAngelis and Skvarca, 2003).
Other glaciers have thinned, accelerated and receded as a result of increased melting (see Recent Change) (Pritchard et al. 2009; Pritchard and Vaughan, 2007). The rapid shrinkage of glaciers around the Antarctic Peninsula, coupled with the potential for ice-shelf collapse and grounding line retreat, raises concerns for the future of the West Antarctic Ice Sheet, and this is an area of urgent current research (Bentley, 2010). This is covered in more detail under Marine Ice Sheet Instability.
Videos to watch
Further reading
- Marine Ice Sheet instability
- Ice shelves
- Sea level rise
- Glacier recession in Patagonia
- Glacier recession on the Antarctic Peninsula
- Glaciers and climate change
- Antarctica’s contribution to global sea level rise
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Actually, a question: In figure 8 above, you show the data streams for methane, temperature and carbon dioxide continuing on a bit to the right of “0” time. The data has a bit of slope, but it must represent only a few years worth of new data, so is the time scale to the right of zero different from that for the past? Another way to ask this question is what actual year is “0?”
I think the succession of figures 6, 7, and 8 is wonderful to have because it shows a succession of time scales. I think the public generally does not pick up on the fact that the “abrupt” temperature and co2 rises
shown for the last 400,000 (or 800,000) years (fig 8) would look extremely gradual, if plotted at 200 years per foot, while our “hockey stick” of today would look the same. Also note one might improve the comparability of these figures if the ”0″s were aligned with the climate consistently. It is to the left of the last serious dip in temperature inf fig 7, to the right in fig 6, and it is tough to say in fig 8.
There are better graphs in the Epica ice core data that clearly show the extreme rise[ accelerating to almost straight up] of the temp/CO2 that started about 200 years ago when we started burning fossil fuels.[A massive change] Till this time for 800,000 years that we can check, the temp/CO2 lines varied up and down a little but stayed closely together and fairly flat, relatively minor variations are seen and expected. Temp and CO2 are very closely connected as you would expect and even as it shot up tney are still closely linked. I cant find the graph now. Looking for it as ime arguing with my brother about climate change brought me here. Its “one” of the best and most easily understoood pieces of the huge amount of data available. Ufortunately this data is very hard for most to understand:/
Historical long term data will repeat – period.
Current extreme rise, if true, holds hope humankind may (?) have hope.
It is obvious that as Earth’s orbit moves away from the sun, temperatures will drop.
All we can do is build very large engines to counteract Earth’s tilt and orbit changes.
Do you have any evidence that the earth is moving away from the sun?
Long-term climate change over (hundreds of) thousands of years is regulated by changes in the Earth’s orbit, called ‘Milankovtich Cycles’. However, there is no sustained movement of the Earth away from the Sun outside of these regular cycles.
🙂
The orbit and tilt of the earth while changing a little over VERY long timescales is negligible in human timescales! If you believe “historical long term data” will repeat, thats at odds with believing the earth is moving away in anything like a speed that will affect things in human scales”/ If this were true, things would cool steadily, not repeat. While some aspects do repeat, seasons, other cycles etc, in the long term these minor repeating cycles exist within long term changes that are not repeating and are caused by many different factors that have no predictable factors[vulcanism, asteroid impact, HUMAN activity etc]. “Current extreme rise” holds hope ??? The opposite is more likely:/ There is NO WAY that WE could possibly build anything that could stabilize something as huge as a planet:/
As per Alschuler’s comment above, I also had wondered about the time scale for the lines continuing off the chart “to the right of year 0”. In radiocarbon dating, BP is normally used to mean Before Present, which has been defined for reference purposes as the year 1950. So I am guessing that this is what 0 on the time axis of this graph represents. The lines to the right thus are obviously drawn on an expanded time scale; presumably, they represent the time from 1950 to the last year noted, 2004, thus, 64 years, plotted on a distance that would otherwise have represented about 10,000 years on the rest of the graph. It would have been “good scientific practice” for the person or website that created, edited, or reproduced this graph, to explicitly state exactly what the scale is for this part of the time axis.
This was very helpful, Thanks you very much sir.
I think you need to explain how maps from the 1500s show Greenland and Antarctica without ice.
This would suggest that your ice is newer than 800,000 years old.
Because the maps were not created in the 1500’s
They are supposedly made from information copied from maps from extremely ancient times.
We know for a fact Antarctica and Greenland had Ice in the 1500’s
1) The vikings did visit greenland earlier and found it quite icy
2) The amount of ice in both places could not possibly appear in a mere 600 years
The map i think you are referring to is the “piri Reis” map. A 15th century copy of a much older map[supposedly] showing Antarcticas coastline as it looks without ice. This does not nescessarily mean it had NO ice. If its genuine, it changes the known history of man completely and who knows when or how, [or if] it was imaged to make this map. Its been covered a long time mostly. At least 800,000 years. So if its real either our entire human chronology is completely wrong and humans have been around a VERY long time[highly unlikely]or an unknown civilization in the past[Atlantis??,lol] imaged it while ice still covered it.[mind boggling] Parts of it show the evidence of its temperate past[plant fossils etc] A LONG time ago the continent, like all others was in a different position. On the equator in fact. Plate tectonics are continually moving the continents around the planet as they float on the molten mantle. There is no doubt thast ice cores show an ice history at least 800,000 years old!
What is the relationship between the sun (sun spot activity) and CO2 levels and global warming or cooling?
Sunspot activity will have little affect on CO2 levels, mostly its an 11 year cycle between peaks. In human time scales the sun affects climate only in a very small way. Over many hundreds of millions of years it has been through periods of warmer and cooler times, but its pretty stable and should stay so for billions more years, warming gradually till the end times when it will start cooling as it finishes burning up its hydrogen, swells up and engulf the inner planets before shrinking into a dim, cool red dwarf. Thats a LOONG way in the future. People will be gone LONG before then:/
I wonder, how you used the data (how it got put together). Did data provided by geologist got mixed in with weather records? That would be unprofessional….
Climate changes all the time, in a small way,it has changed in a big way in the distant past. Variations occur for many reasons but up till 200 odd years ago the changes were fairly minor during the last 800,000 years, some are cyclical caused by things like the “Milankovich cycle” , asteoid impact, vulcanism and even the seasons, and many other reasons, but their are ALWAYS reasons!! Even ice ages are only blips in the larger scheme of things. These are small variations in the larger scheme of things. This time there is no doubt that its OUR activitys that are changing it. I cannot understand the passion of man made climate change deniers when its very obvious and logical that the massive amount of CO2 and methane etc that we have dumped into the atmosphere since we started the industrial revolution has changed things big time. Look at the Epica ice core data from Antarctica.. For 800,000 years the graph of temp/CO2 wobbled along up and down in a small way, Even the last ice age made little difference in the big picture. Then comes the start of the IR… The graph of temp/CO2 correlation in the ice cores that for all that time was pretty stable suddenly starts heading straight up in a very major shift that is unheard of in a million years. This is a short time in the life of the earth, and major changes have of course occured over the billions of years the earth has existed,always with causal agents, but the change that started sending the climate beserk 200 years ago just as we started our massive polluting activitys is too big to be coincidence. This cannot be argued against. We ARE changing the climate in a huge way, and its now reached the point of being too late to stop:/ How can anyone with a brain believe that dumping the huge amount of greenhouse gasses into the atmosphere that we have for 200 years cannot affect the climate?. All the fossil fuels we have burned took many millions of years to form, locking up the gasses safely for all that time, till we released them. To think this has had no effect is ridiculous. Blaming “natural” change is laughable and illogical:/ AS our fuels run out we will seek the next, it will be methane hydrate,[nuclear has proved a disaster as we are too careless to do it right] massive amounts of it are locking up methane from the decay of ancient forests just as oil did in a different way:/ The ocean bottoms are littered with it! Its very clean, much more so than oil but still will release massive amounts of CO2 and methane. I shudder to think what THAT will do to the already out of control climate! Ime far from stupid, in fact ime in the top 2% intelligence wise, so is my brother but he denies manmade climate change. If he can, its no suprise that your average human can:/ People in general prefer to put their heads in the sand when it comes to things that may affect their comfortable lives, regardless of the consequence:( Its too late to go back, but we can mitigate further changes, but at “some” cost to our comfortable lives. People in general do not want this, they are basically selfish for the most part and only care about “THEIR” lives, not the future, or, they do not think about it, or if they do they rationalize, ignore, play down, or ignore and deny the consequences. Heads in sand:/ I dont think much of the human race, its time is coming to an end, no loss:/ The earth will recover and maybe a more deserving race will get their chance. Our stewardship of this beautiful planet has been a disaster, ime afraid that your average human is far too stupid, self centered and immature. Evolution has brought us to the point where we are intelligent enough[SOME of us] to affect things disasterously, but most are not intelligent[or caring] enough to predict [or if they can, care ]about the consequences of our actions. The few that are aware are shouted down by the masses. What a pathetic bunch of losers:( War, famine, disease, overpopulation, pollution…Humans are very akin to one other lifeform on earth…A VIRUS. We consume, we breed, till resources are exhausted then we move on and do the same again. Well, what happens to a virus?? It eventually consumes all and burns out, our eventual fate in a nutshell:/ God help the universe if we somehow manage to get off this planet before this occurs, but i doubt that its likely, thankfully:/
A simple question from a layman.
Most mineral resources are being mined from the southern hemisphere and shipped to the northern hemisphere.
There is no reverse action to counteract this.
So in effect we are putting the ball out of balance which would affect its rotation.
What effect could this have on global warming and climate change.
It would only need to be a small amount out of balance to put the planet out of position over a long term
Not even in the rounding error
US
No doubth, global temperature is rising, no doubth, carbon dioxide in atmosphere is rising. If we consider burning of fossil fuels as a reason, we need to explain following: Carbon isotope ratio in organic matter (fossil fuels) is in average -25, in atmosphere in average -7. So emission of carbon dioxide from burning of fossil fuels need to change isotope ratio in atmosphere. During recent 50 years carbon isotope ratio in atmosphere has changed from -6.7 to -7.3 – less than 10 %. At the same time carbon dioxide concentration in atmosphere has rised 30%. Calculating more precisely we see, that burning of organic material could account no more than 20% of the rise of carbon dioxide concentration in the atmosphere. Please explain me this contradiction.
I’m not knowledgeable enough to say anything definitively, but I remember hearing that CO2 from livestock is a substantial part of our CO2 emissions. I’m not sure if those would have the same carbon isotope ratio as our atmosphere naturally does (or how much closer it would be, if not), but that’s clearly a factor that could indicate much higher contributions to CO2 concentrations due to human endeavors.
To be accurate, you would also need to quantify the expected populations of our various livestock, to compare, as well as physiological changes that may have altered the average CO2 emissions of those animals we’ve domesticated. On the same subject, displacement of other animals would be a clear, if marginal, factor; other animals that could’ve taken our space would have contributed some amount of CO2.
Physiological changes could be marginal, but the population estimations would be difficult, perhaps tenuous, to quantify. Domestication has increased instantaneous populations of many animals, though, so I’d presume it would be a substantial factor to weaken the calculated affect of livestock. It’s not completely implausible, though, that we have disrupted certain ecosystems that would have virtually unknowable affects on atmospheric composition.
I do not know how much of an impact these numbers would indicate, but it almost certainly would indicate a greater contribution, overall, of human works. It probably will also indicate a greater contribution directly from fossil fuel burning. Definitive indications would require the scope of an entire study of work, to be thorough, I feel.
carbon dioxide is also absorbed by trees/ocean every year – so a large % of the CO2 that was created with burning fossil fuels is absorbed, this would reduce the carbon isotope ratio. Its absorbed then also released – but the release is a different isotope, and the net effect is more CO2 because the amount released isnt what was absorbed.. .
i hope that clears it up and makes sense?
On the ice core chart, there are steep inclines followed by steep declines. Can anyone enlighten me on how science explains this? It came up in an office discussion and I couldn’t give a good answer.
Very cool idea! Excellent job. I spent the last 20 minutes having a good read of your content.
I like how at the exact point that the greenhouse effect and modern warming was discovered, suddenly the temp just shoots up like a rocket lol.