Reblogged from Real Science:
Understanding The 1979 Arctic Ice Cherry Pick
Posted on February 22, 2014 by stevengoddard
Climate fraudsters like to claim that Earth began in 1979, the year of peak Arctic sea ice. The graph below shows why. If they started their graph in 1954, there would be almost no downwards trend to the present.
journals.ametsoc.org/doi/pdf/10.1175/1520-0485(1979)009<0580>2.0.CO%3B2
Reblogged from Global Warming Solved:
Ice trends
The satellite records only began in October 1978, however. This coincided with the start of a recent warming trend in the Arctic. Before that, from the 1950s-1970s, Arctic temperatures were cooling. So, it is quite likely that in the decades immediately before the satellite records began, average Arctic sea ice extent was actually increasing, but we just weren’t monitoring it. It seems that the Arctic sea ice extent naturally goes through periods of expansion, followed by periods of contraction.
In case you’re unsure about which is which, the Arctic is the polar region in the north (the one with polar bears, etc.) and the Antarctic is the polar region in the south (the one with penguins, etc.)
In this essay, we look at what we know about Arctic sea ice extent.
1. The satellite era
2. What do we know about Arctic temperatures?
3. The pre-satellite era
4. The great Arctic explorers
5. Conclusions
1. The satellite era
Every winter, the sea ice in the polar regions grows, but then in the summer, it melts again.
Figure 1. Minimum and maximum sea ice extents for northern and southern hemispheres in 1979. Click to enlarge.Since winter and summer are reversed between the southern and northern hemispheres, this means that as the Arctic sea ice reaches its maximum extent in March, the Antarctic sea ice is reaching its minimum extent. By September, the situation has reversed (minimum Arctic and maximum Antarctic sea ice). This can be seen from the Google Earth images in Figure 1 (generated using data from NSIDC).
Figure 2. Trends in maximum (March), minimum (September) and average annual sea ice extents for the Arctic, since records began in 1979. Error bars for the average value correspond to the standard errors. Click to enlarge.This cyclical pattern occurs every year. However, since satellite records began in 1979, the maximum (March) and minimum (September) sea ice extents in the Arctic seem to have been gradually decreasing. This can be seen from Figure 2 (generated using NSIDC data).
This has led many people to worry that it is man-made global warming which is causing the Arctic sea ice to melt, and that humans are therefore destroying an entire ecosystem, threatening animals such as polar bears.
As a result, much of the research in the Arctic in recent years has become dominated by a heavy focus on man-made global warming, rather than studying the Arctic as a fascinating region in itself.
Figure 3. Trends in maximum (September), minimum (March) and average annual sea ice extents for the Antarctic, since records began in 1979. Error bars for the average value correspond to the standard errors. Click to enlarge.Interestingly, even though you might expect “global” warming to occur globally, in the southern half of the world, the Antarctic sea ice extent doesn’t seem to have changed much (see Figure 3). This apparent paradox has puzzled those who believe the Arctic melting is due to man-made global warming.
As a result, some groups have struggled to come up with explanations as to why man-made global warming is not causing melting of Antarctic sea ice. For example, Zhang, 2007 (Open access) proposed that warmer waters off Antarctica might make the water less salty, and that maybe this would stop the ice from melting. We believe a much simpler explanation is that the changes in the Arctic sea ice arenot due to the “man-made global warming” assumed by current climate models. If the explanation is not “CO2-related”, then we would no longer need to worry about why the models don’t match the data – it would just mean that the models are wrong.
At any rate, since the Antarctic sea ice extent doesn’t seem to be declining, the public concern over sea ice seems to be confined to the Arctic. With that in mind, let us limit our discussion in this essay to the Arctic, i.e., the region which has shown a decrease in polar sea ice. The fact that the Arctic sea ice seems to have been steadily decreasing “since records began” does initially seem alarming. However, as we will see below, this is because “the records” only began in October 1978, as the satellites weren’t launched until then.
There may be some problems with the satellite estimates of sea ice extent, e.g., see here. Estimating sea ice extent from satellites is a complex problem – the satellites aren’t actually photographing the amount of ice, so it’s not a simple case of looking at a photograph and saying “oh, there’s some ice there, and none there”.
Instead, they measure microwave emissions. Analysts then try to convert those measurements into estimates of sea ice. These conversions rely on several different assumptions being valid. If there are problems with those assumptions, it may affect the reliability of the satellite estimates.
However, for the purposes of this post, we assume that the satellite estimates are reliable.
2. What do we know about Arctic temperatures?
Figure 4. Top panel: Unadjusted average temperature trends of all GHCN stations in the Arctic Circle. Thick solid line corresponds to a smoothed average (11 point binomial). Bottom panel: Number of stations available in a given year. Taken from our Urbanization bias III paper. Click to enlarge.In Figure 4, the average annual temperature trends for the Arctic are shown (the graph is taken from our “Urbanization bias III” paper – Provide link!). We can see that there has indeed been a warming trend since the late 1970s. However, if we look at the rest of the data, the problem of the sea ice record only beginning in 1979 should become obvious – the warming trend since the 1970s followed acooling trend from the 1940s. If the sea ice records had started just a bit earlier, they would probably have first shown sea ice growth!
Before the 1940s-1970s Arctic cooling, there also seems to have been another warming period (1900s-1930s). We do not have enough weather records to reliably tell what happened to Arctic temperatures before the 20th century, but it is at least plausible that similar cooling and warming periods also occurred then. It seems that temperatures in the Arctic naturally alternate between periods of warming and periods of cooling.
In the next sections, we will argue that sea ice conditions in the late 1970s were relatively severe. So, the fact that the Arctic sea ice extent seems to have been decreasing since then is not an indicator of “unusual and dramatic melting of the Arctic”. Instead, it seems that the satellite monitoring of the Arctic sea ice just coincidentally started at the wrong time, i.e., just when the last Arctic cooling period had ended!
But before we get to that, some readers might say, “If you look at the graph of Arctic temperatures since 1880, the linear trend shows warming, so that must be due to human activity!”. Well, no.
First, the trends are non-linear, so the “linear trend” is irrelevant. There are periods of both warming and cooling, so the linear trend changes depending on where you start and end your analysis. If you want to, you can technically calculate a “linear trend” for any (x,y) dataset, but if it is non-linear data, as is the case here, then it is a meaningless calculation. See our “Urbanization bias I” paper for more discussion (Provide link!).
Second, there is no reason to assume warming must be “man-made”, rather than just a natural occurrence. For instance, Prof. Syun-Ichi Akasofu, the founding director of the International Arctic Research Center (retired in 2007) argues that the world may still be recovering naturally from the Little Ice Age of the 18th and 19th centuries. Dr. Willie Soon has found that the warming and cooling trends in the Arctic are actually strongly correlated to changes in solar activity, e.g., Soon, 2009 (Abstract; Google Scholar access).
Figure 5. Locations of stations used for constructing the above graph. The 6 stations with data for at least 75 of the last 80 years are shown with white squares. Click to enlarge.Finally, as we discuss in our “Urbanization bias III” paper (Provide link!), there are very few stations with long records available for the Arctic (see the bottom panel of the earlier figure showing Arctic temperature trends). The map in Figure 5 shows the locations of all the available stations – only six of the stations have data for 75 of the last 80 years, and five of them are from a relatively small region (northern Scandinavia).
This means that if there are non-climatic biases in any of the station records, it could strongly alter the apparent trends of the average “Arctic temperatures”. This is a particular concern for periods when the number of stations were very low, e.g., there appears to have been a sudden warming step change at about 1920, but there were only a few stations actually available then, so it is hard to know if the apparent step change was genuinely climatic.
For example, many of the Arctic stations are airport stations, and improvements in the airport infrastructure, such as insulation of permafrost-based runways (e.g., Instanes & Mjureke, 2005) could easily have introduced warming biases in recent decades.
Also, you might not think urbanization bias would be a major problem in the Arctic, since most of the big cities are at lower latitudes. But, in tundra conditions, even modest urbanization can introduce significant biases.
Figure 6. Comparison of temperature trends for two of the six Arctic stations with relatively long and complete records. Thick solid lines correspond to smoothed averages (11 point binomial). Taken from our Urbanization bias III paper. Click to enlarge.For instance, even though Barrow, Alaska (USA) still has a relatively small population (4,500 in 2000), urbanisation has led to a considerable urban heat island there in recent years – see Hinkel et al., 2003(Open access). This would have introduced an artificial warming trend which would make the recent warm period seem warmer than it actually was. In comparison, the rural Sodankylä, Finland station also shows a warming trend since the late 1970s, but it followed a cooling period from the 1940s, and its warmest year was actually in 1937 (see Figure 6).
So, unfortunately, the data is really too limited to make definite conclusions (e.g., only six stations with data for 75 of the last 80 years, and at least one of them is known to have an urban heat island). It may well be that the recent warm period was warmer than the early 20th century warm period, as the raw data suggests… Or it may be that biases in the raw data are substantial, and the early 20th century warm period was just as warm as the recent warm period, or maybe even warmer.
Whatever the case, it is clear that the Arctic seems to alternate between periods of warming and periods of cooling. Hence, the fact that “the Arctic sea ice has been decreasing since records began” is merely down to the fact that the records only began in 1978. In the next sections, we will try to estimate how sea ice varied, before the satellite era.
3. The pre-satellite era
A few groups have attempted to construct sea ice estimates for the pre-satellite era using various combinations of land, ship, submarine, buoy and aircraft measurements made over the years, e.g., the Chapman & Walsh dataset or the Zakharov dataset (Note that the server for the Zakharov dataset is not always online, so the link sometimes doesn’t work). These datasets represent a considerable amount of compilation work, and probably could be used to extract useful climate information. But, as we will discuss below, there are too many inconsistencies in the data sources for a simple analysis.
Some people have used these datasets to argue that the decreasing trend during the satellite era is an acceleration of an already decreasing trend in the pre-satellite era. For instance on the “Open Mind” blog, the blogger “Tamino” has used the Walsh & Chapman dataset to claim that the satellite era melt is unprecedented, e.g., here. However, these datasets should not be used for estimating long term trends. The problem is that such datasets are actually composite datasets constructed by compiling together as many measurements as the researchers can for a given year.
The measurement sources vary dramatically over the years. For instance, in Siberia, measurements up until the late 1930s were mostly from shipping lane reports, while after the late 1930s they mostly came from aircraft measurements. In addition, the actual regions with available data varied substantially over the decades. So, a sea ice estimate for a region constructed from shipping reports in the 1920s might not be directly comparable to an estimate for the same region from the 1940s made from aircraft measurements. Hence, they cannot be used for calculating long term trends.
We suspect that with careful work and calibration, it might be possible to construct useful long term trends for at least part of the pre-satellite era. However, they don’t seem to be reliable yet. For example, we saw in the previous section, that the temperature records show a period of substantial warming followed by a period of substantial cooling up to the satellite era. But, pre-satellite sea ice datasets such as Walsh & Chapman’s don’t show any of that variability in the pre-satellite era.
So, unfortunately, we can’t use the pre-satellite estimates for assessing how unusual the recent melting has (or hasn’t) been. Fortunately, there are ways of assessing how unusual the sea ice in 1979 (at the start of the satellite era) was. If the claim that the recent Arctic melting is unusual and due to man-made global warming were true, then this would mean that the sea ice extent in September 1979 was relatively low (September being the month of minimum sea ice in the Arctic).
In the following section, we will assess this claim, by trying to answer the question, “Would the great 19th and early 20th Arctic explorers have been able to carry out all their voyages if they had attempted it during 1979 conditions?” If September 1979 sea ice extent was already quite low, then 1979 conditions would have been relatively easy for them. However, as we will see, many of the early explorers managed to get much further than they could have in 1979. In other words, at the time of those voyages, the sea ice extent was probably much lower than it was at the start of the satellite era.
The satellite records only began in October 1978, however. This coincided with the start of a recent warming trend in the Arctic. Before that, from the 1950s-1970s, Arctic temperatures were cooling. So, it is quite likely that in the decades immediately before the satellite records began, average Arctic sea ice extent was actually increasing, but we just weren’t monitoring it. It seems that the Arctic sea ice extent naturally goes through periods of expansion, followed by periods of contraction.
In case you’re unsure about which is which, the Arctic is the polar region in the north (the one with polar bears, etc.) and the Antarctic is the polar region in the south (the one with penguins, etc.)
In this essay, we look at what we know about Arctic sea ice extent.
1. The satellite era
2. What do we know about Arctic temperatures?
3. The pre-satellite era
4. The great Arctic explorers
5. Conclusions
1. The satellite era
Every winter, the sea ice in the polar regions grows, but then in the summer, it melts again.
Figure 1. Minimum and maximum sea ice extents for northern and southern hemispheres in 1979. Click to enlarge.Since winter and summer are reversed between the southern and northern hemispheres, this means that as the Arctic sea ice reaches its maximum extent in March, the Antarctic sea ice is reaching its minimum extent. By September, the situation has reversed (minimum Arctic and maximum Antarctic sea ice). This can be seen from the Google Earth images in Figure 1 (generated using data from NSIDC).
Figure 2. Trends in maximum (March), minimum (September) and average annual sea ice extents for the Arctic, since records began in 1979. Error bars for the average value correspond to the standard errors. Click to enlarge.This cyclical pattern occurs every year. However, since satellite records began in 1979, the maximum (March) and minimum (September) sea ice extents in the Arctic seem to have been gradually decreasing. This can be seen from Figure 2 (generated using NSIDC data).
This has led many people to worry that it is man-made global warming which is causing the Arctic sea ice to melt, and that humans are therefore destroying an entire ecosystem, threatening animals such as polar bears.
As a result, much of the research in the Arctic in recent years has become dominated by a heavy focus on man-made global warming, rather than studying the Arctic as a fascinating region in itself.
Figure 3. Trends in maximum (September), minimum (March) and average annual sea ice extents for the Antarctic, since records began in 1979. Error bars for the average value correspond to the standard errors. Click to enlarge.Interestingly, even though you might expect “global” warming to occur globally, in the southern half of the world, the Antarctic sea ice extent doesn’t seem to have changed much (see Figure 3). This apparent paradox has puzzled those who believe the Arctic melting is due to man-made global warming.
As a result, some groups have struggled to come up with explanations as to why man-made global warming is not causing melting of Antarctic sea ice. For example, Zhang, 2007 (Open access) proposed that warmer waters off Antarctica might make the water less salty, and that maybe this would stop the ice from melting. We believe a much simpler explanation is that the changes in the Arctic sea ice arenot due to the “man-made global warming” assumed by current climate models. If the explanation is not “CO2-related”, then we would no longer need to worry about why the models don’t match the data – it would just mean that the models are wrong.
At any rate, since the Antarctic sea ice extent doesn’t seem to be declining, the public concern over sea ice seems to be confined to the Arctic. With that in mind, let us limit our discussion in this essay to the Arctic, i.e., the region which has shown a decrease in polar sea ice. The fact that the Arctic sea ice seems to have been steadily decreasing “since records began” does initially seem alarming. However, as we will see below, this is because “the records” only began in October 1978, as the satellites weren’t launched until then.
There may be some problems with the satellite estimates of sea ice extent, e.g., see here. Estimating sea ice extent from satellites is a complex problem – the satellites aren’t actually photographing the amount of ice, so it’s not a simple case of looking at a photograph and saying “oh, there’s some ice there, and none there”.
Instead, they measure microwave emissions. Analysts then try to convert those measurements into estimates of sea ice. These conversions rely on several different assumptions being valid. If there are problems with those assumptions, it may affect the reliability of the satellite estimates.
However, for the purposes of this post, we assume that the satellite estimates are reliable.
2. What do we know about Arctic temperatures?
Figure 4. Top panel: Unadjusted average temperature trends of all GHCN stations in the Arctic Circle. Thick solid line corresponds to a smoothed average (11 point binomial). Bottom panel: Number of stations available in a given year. Taken from our Urbanization bias III paper. Click to enlarge.In Figure 4, the average annual temperature trends for the Arctic are shown (the graph is taken from our “Urbanization bias III” paper – Provide link!). We can see that there has indeed been a warming trend since the late 1970s. However, if we look at the rest of the data, the problem of the sea ice record only beginning in 1979 should become obvious – the warming trend since the 1970s followed acooling trend from the 1940s. If the sea ice records had started just a bit earlier, they would probably have first shown sea ice growth!
Before the 1940s-1970s Arctic cooling, there also seems to have been another warming period (1900s-1930s). We do not have enough weather records to reliably tell what happened to Arctic temperatures before the 20th century, but it is at least plausible that similar cooling and warming periods also occurred then. It seems that temperatures in the Arctic naturally alternate between periods of warming and periods of cooling.
In the next sections, we will argue that sea ice conditions in the late 1970s were relatively severe. So, the fact that the Arctic sea ice extent seems to have been decreasing since then is not an indicator of “unusual and dramatic melting of the Arctic”. Instead, it seems that the satellite monitoring of the Arctic sea ice just coincidentally started at the wrong time, i.e., just when the last Arctic cooling period had ended!
But before we get to that, some readers might say, “If you look at the graph of Arctic temperatures since 1880, the linear trend shows warming, so that must be due to human activity!”. Well, no.
First, the trends are non-linear, so the “linear trend” is irrelevant. There are periods of both warming and cooling, so the linear trend changes depending on where you start and end your analysis. If you want to, you can technically calculate a “linear trend” for any (x,y) dataset, but if it is non-linear data, as is the case here, then it is a meaningless calculation. See our “Urbanization bias I” paper for more discussion (Provide link!).
Second, there is no reason to assume warming must be “man-made”, rather than just a natural occurrence. For instance, Prof. Syun-Ichi Akasofu, the founding director of the International Arctic Research Center (retired in 2007) argues that the world may still be recovering naturally from the Little Ice Age of the 18th and 19th centuries. Dr. Willie Soon has found that the warming and cooling trends in the Arctic are actually strongly correlated to changes in solar activity, e.g., Soon, 2009 (Abstract; Google Scholar access).
Figure 5. Locations of stations used for constructing the above graph. The 6 stations with data for at least 75 of the last 80 years are shown with white squares. Click to enlarge.Finally, as we discuss in our “Urbanization bias III” paper (Provide link!), there are very few stations with long records available for the Arctic (see the bottom panel of the earlier figure showing Arctic temperature trends). The map in Figure 5 shows the locations of all the available stations – only six of the stations have data for 75 of the last 80 years, and five of them are from a relatively small region (northern Scandinavia).
This means that if there are non-climatic biases in any of the station records, it could strongly alter the apparent trends of the average “Arctic temperatures”. This is a particular concern for periods when the number of stations were very low, e.g., there appears to have been a sudden warming step change at about 1920, but there were only a few stations actually available then, so it is hard to know if the apparent step change was genuinely climatic.
For example, many of the Arctic stations are airport stations, and improvements in the airport infrastructure, such as insulation of permafrost-based runways (e.g., Instanes & Mjureke, 2005) could easily have introduced warming biases in recent decades.
Also, you might not think urbanization bias would be a major problem in the Arctic, since most of the big cities are at lower latitudes. But, in tundra conditions, even modest urbanization can introduce significant biases.
Figure 6. Comparison of temperature trends for two of the six Arctic stations with relatively long and complete records. Thick solid lines correspond to smoothed averages (11 point binomial). Taken from our Urbanization bias III paper. Click to enlarge.For instance, even though Barrow, Alaska (USA) still has a relatively small population (4,500 in 2000), urbanisation has led to a considerable urban heat island there in recent years – see Hinkel et al., 2003(Open access). This would have introduced an artificial warming trend which would make the recent warm period seem warmer than it actually was. In comparison, the rural Sodankylä, Finland station also shows a warming trend since the late 1970s, but it followed a cooling period from the 1940s, and its warmest year was actually in 1937 (see Figure 6).
So, unfortunately, the data is really too limited to make definite conclusions (e.g., only six stations with data for 75 of the last 80 years, and at least one of them is known to have an urban heat island). It may well be that the recent warm period was warmer than the early 20th century warm period, as the raw data suggests… Or it may be that biases in the raw data are substantial, and the early 20th century warm period was just as warm as the recent warm period, or maybe even warmer.
Whatever the case, it is clear that the Arctic seems to alternate between periods of warming and periods of cooling. Hence, the fact that “the Arctic sea ice has been decreasing since records began” is merely down to the fact that the records only began in 1978. In the next sections, we will try to estimate how sea ice varied, before the satellite era.
3. The pre-satellite era
A few groups have attempted to construct sea ice estimates for the pre-satellite era using various combinations of land, ship, submarine, buoy and aircraft measurements made over the years, e.g., the Chapman & Walsh dataset or the Zakharov dataset (Note that the server for the Zakharov dataset is not always online, so the link sometimes doesn’t work). These datasets represent a considerable amount of compilation work, and probably could be used to extract useful climate information. But, as we will discuss below, there are too many inconsistencies in the data sources for a simple analysis.
Some people have used these datasets to argue that the decreasing trend during the satellite era is an acceleration of an already decreasing trend in the pre-satellite era. For instance on the “Open Mind” blog, the blogger “Tamino” has used the Walsh & Chapman dataset to claim that the satellite era melt is unprecedented, e.g., here. However, these datasets should not be used for estimating long term trends. The problem is that such datasets are actually composite datasets constructed by compiling together as many measurements as the researchers can for a given year.
The measurement sources vary dramatically over the years. For instance, in Siberia, measurements up until the late 1930s were mostly from shipping lane reports, while after the late 1930s they mostly came from aircraft measurements. In addition, the actual regions with available data varied substantially over the decades. So, a sea ice estimate for a region constructed from shipping reports in the 1920s might not be directly comparable to an estimate for the same region from the 1940s made from aircraft measurements. Hence, they cannot be used for calculating long term trends.
We suspect that with careful work and calibration, it might be possible to construct useful long term trends for at least part of the pre-satellite era. However, they don’t seem to be reliable yet. For example, we saw in the previous section, that the temperature records show a period of substantial warming followed by a period of substantial cooling up to the satellite era. But, pre-satellite sea ice datasets such as Walsh & Chapman’s don’t show any of that variability in the pre-satellite era.
So, unfortunately, we can’t use the pre-satellite estimates for assessing how unusual the recent melting has (or hasn’t) been. Fortunately, there are ways of assessing how unusual the sea ice in 1979 (at the start of the satellite era) was. If the claim that the recent Arctic melting is unusual and due to man-made global warming were true, then this would mean that the sea ice extent in September 1979 was relatively low (September being the month of minimum sea ice in the Arctic).
In the following section, we will assess this claim, by trying to answer the question, “Would the great 19th and early 20th Arctic explorers have been able to carry out all their voyages if they had attempted it during 1979 conditions?” If September 1979 sea ice extent was already quite low, then 1979 conditions would have been relatively easy for them. However, as we will see, many of the early explorers managed to get much further than they could have in 1979. In other words, at the time of those voyages, the sea ice extent was probably much lower than it was at the start of the satellite era.
You had -800 000 km2 anomalies in the 1960's. Wow. Only that the anomalies in 2000's was as much as 3 million km2!
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