About this page
A survey of the science of climate change with some comments on what it might mean for saiors - in the longer term.
Theis article was first written in 2004 with subsequent amendments. For the latest information go to the Hadley Centre Website. Athough government funded the Ccentre is free from political or commercial/ business pressures. A source of useful and informed information is the American Institute of Physics.
Since 2004, the science has advanced, computer are more powerful. Thre are now more data and a better understanding od both the science and its limitations. The Intergovernmental Panel on Climate Change 5th Report includes a section on , The Physical Science Basis. The science and the conclusions have been summarised by the US National Academy of Science and the Royal Society. This is aimed at the non-specialist.
A UK Met Office report on The Storms of 013/4 and Floods in the UK puts these events into a global perspective and gives an insight into how climate change might affect wather detail..
A Met Office report studiies the Recent Paue in Global Warming and explains why this does not invalidet the IPCC main finding that man is affecting climate. The appendices are very informative.
Globally, 2014 was one of the warmest years on record. In fact, 13 of the 14 warmest years have occurred in the 21st Century. To put recent eents into context, the following are well worth reading.
- Public perceptions
- Who are the experts
- Climate - what are the arguments
- Snow in the UK - is it so unusual?
- Some Climate Data
On this page -
- The Questions
- The Problems
- Surrogate data
- CO2 – Temperature Correlation
- Computing Climate
- The Results
- Effects on Sailors?
- The bottom line
Click on thumbnails to see diagrams.
I am not an expert on global warming but, in my Met Office days I was in close working contact with those in the field. This article has been produced partly, and unashamedly, using output from the Hadley Centre, now regarded as a world leader on this most important topic and the IIPCC AR5, WGl 1 latest report.
Significant advances in meteorology have always required the largest computers available. Current computers used have speeds of well over 1018 flops (floating arithmetic operations per second). It has been estimated that to compete with the atmosphere on level terms would need an increase in speed of 1036.
Comsequently, the major centres capable of undertaking climate research have to be funded by governments. In the IPCC AR5, there are some 18 centres listed. These are the main authoritative sources of assessments of climate change although there are many other centres, including university departments capable of assessing, criticising and contributing to the science and its application. It follows that the results quoted here have all been subjected to critical peer review.
Is climate changing? The answer must alw ays be "Yes". Climate has always been changing. But, the impotent questions are:
- Are the current changes really unusual?"
- Why is it changing
- Is man responsible?"
- And, if so can any action be taken?"
Like so often in meteorology, these apparently simple questions are extremely complex. Statistical analyses may point at possible reasons and mechanisms but real understanding can only come from studying the many physical processes and feedbacks. These are summarised on my page about Numerical Weather Prediction.
The “greenhouse effect” refers to sinlight passing through the atmosphere like though a glass window while some of the long wave radiation from the earth is absorbed by gases in the atmosphere. The difference in using weather models for climate prediction is the incorporation of factors that can change the processes described.
An important question is,
- “Can those qualitative descriptions
be used quantitatively to describe climate change as they do for day-to-day forecasting?”
This is necessary if findings, which may be unpalatable to some, are to carry weight and lead to any action that may be possible. Accordingly, theories of the physical, biological and chemical processes of the atmosphere should be scientifically sustainable. In effect, the science has to be able to account for the observed changes and predict the future.
Conversely, arguments that question or deny such man-made effects should also be able to withstand scientific scrutiny.
Hadley Centre Scientists and those from many other groups in many other countries contributing to the IPCC Scientific Assessment reports, say, with true scientific caution, that all the indications are that man is having an adverse effect. The next question is
- "What will it mean for us?"
The atmosphere is complex in that all the driving forces are highly interactive. The sun heats the earth which then heats the atmosphere. This is by
- Conduction leading to
- Radiation and
- Latent heat when water freezes/melts or condenses/evaporates.
These processes are illustrated in this diagram:
(From IPCC AR5, Woking Group 1 Report, Chapter09_FINAL.pdf Chapter 9, 1913.) Outgoing infrared radiation is absorbed by the greenhouse gases, primarily water vapour, CO2, CH4 , various industrial gases and ozone (O3). Infrared radiation is also absorbed and mitted by aerosols that come naturally from volcanoes, from dry land and outer space. Man inputs aerosols from industry and other activities. Overall, aerosols have a net cooling effect.
On timescales of varying lengths, heat input from the sun can change. This can be due to variation in emissivity eg sunspots with a cycle of around 11 years. There are variations on much longer time scales due to the tilt of the earth and in its orbit round the sun.
Causes for our ever changing climate can be put into two brad categories, internal and external forcing. . Internal factors result from phenomena such as El Niño and La Niña, air/sea interactions generally, polar ice variability etc. External factors can be manmade such as greenhouse gas emissions and dust from industry and agriculture. Other effects can come from volcanic activity, interstellar dust, variations in soar radiation.
Some of these lead to short term varaiability. Some, particularly changes in greenhouse gases may be long lived. Some, sunspot cycles may be cyclic in nature.
The results are well shown here -
There is an obvious upward trend in greenhouse gases but the rise in global temperatures is much more variable. This leads to understandable doubts and is a factor used by those that doubt that man is affecting the climate.
Sources of Information - What They Tell Us -
The earliest known weather observations were from China around 1000 BC but the records are descriptive and qualitative rather than instrumental and quantitative. There are rainfall data from the area of the Indus Delta some time later but there are problems in using these in relation to modern measurements. Rainfall, by its very nature is a difficult parameter to use for the purposes of studying climate.
The most useable instrumental data are of temperature. Some of the longest near homogeneous records (dating back to the 17th century) are from the Central England (CET¬) series. This record has been compiled using data from different instruments and locations but with much effort, The series was initiated by Professor Gordon manley in the 1950s. The Hadley Centre now maintains this quasi-homogeneous record.
See the Hadley Centre website for details. The red line is a filter that gives, effectively, a 10 year running mean.
Such records are clearly useful but are insufficient to make any sensible deductions on a world-wide scale. A major problem with land based observations of weather, particularly temperature, is to eliminate the effects of changes in land use and other local human activity.There are ways of making allowance for these factors but it is all too easy for the deductions from the data to be discounted.
Observations over the oceans do not suffer from these drawbacks although, even here, the derivation of climatological data capable of rigorous scrutiny is by no means straightforward. Observing weather from ships began to be organised on an international basis in the mid 1850s.
The number of ships providing weather data increased over time although in recent years the numbers have decreased. Over time, observing practices have changed. Initially, water was pulled up in a canvas bucket. Later, moreconsistent data were obtained fro the engine cooling water intake. This is still used but with even more consistent data still from satellites.
A major project in the Met Office, over many years, studied the effects of changing measurement techniques and of varying tracks of ships. Practical experimentation and statistical techniques were used in combination. One of many problems is the merging if satellite observations that “see” just the sea surface with cooling water intake data that are from below the surface. Data series have been derived to study changes in sea surface temperature since the start of the data series.
Recent studies have shown that the higher sea temperatures extend well below the ocran surface.as shown here.
More detail of measuting techniques and results can be seen at A review of global ocean temperature observations: Implications for ocean heat content estimates and climate change
It is difficult to overestimate the importance of ocean temperature measurements for persons who are attempting to understand the present and future impacts of human emissions on the climate. A long-term high-quality record of ocean temperature observations is crucial for constraining our understanding of climate change. This is particularly so since the oceans are responsible for the majority of heat uptake and thermal buffering. This manuscript serves as a historical perspective and a future road map for the oceanographic community.
To get longer data records is a problem that has been tackled using "proxy" data. These rely upon information derived from a variety of sources such as width and density of tree rings, sediment or ice cores and fossil remains. Archaeological digs in human settlements can tell us about what crops were grown or what wild plants they used. These are good pointers to the climate of the time. Ice and sediment cores can tell us not only about the prevailing climate but also the constituents of the atmosphere. Fossil remains can give information on animals and plants at different times in history and, again, provide valuable climate indicators.
Palaeoclimatology, the interpretation of the data is a science in its own right but there are large error bars. Some verification can be obtained back to about 1000 BC due to documentary records kept in China. The totality of techniques is rather like a three dimensional jigsaw of inestimable complexity. This figure shows, data over different areas compiled from AD 900 to 2004,
NOAA/NCDC Temperature changes through ice ages, The blue lines are a reconstruction of the temperature. The red lines reconstructions of CO'^2^.
The next figure shows a reconstruction of CO2 over the same period.
From the NOAA page Climate change: How do we know?
There is good factual evidence that the 20th century warming trend is continuing. 2014 was the warmest year on record globally and 13 0f the warmest years have occurred since 2000.
This fact, in itself, may not be too significant looked at on time scales stretching back over millennia. However, the climatologists have been able to show that the rate of change is highly statistically significant and not likely to be attributable to normal climate variability.
Recent surrogate evidence can be seen in the length of the growing season in the UK. Other indicators are seen in bird migration and insect occurrence. Bee keepers will tell you that they are seeing swarming of bees much earlier than in the recent past.
Correlation between CO2' and Temperature
There is a clear and significant correlation between amounts of CO2 in the atmosphere and global temperature as. This cane beseen here from the Climate Center site
Simple linear regression of atmospheric CO2 concentrations on HadCRUt temperatures from 1980 to 2002 in red, as well as the line of best fit for the data projected out through 2009. 2003 to 2009 observations are shown in blue so they can be evaluated in light of the prior trend without influencing it. The figure above shows a linear regression of temperature on CO2 concentration, and also the projection one would expect of 2003 to 2009 CO2 concentrations given the relationship between the two factors from 1980 to 2002. (From theYale Climate Connections site)
Computing the Climate
However, the existence of a statistical correlation is not proof of a physical connection.
To determine whether these trends are due to the activity of man, the scientists use mathematical models broadly similar to those used in day to day weather prediction. The differences are that they have to take into account all the factors involved in driving the atmosphere. These include changes in-
- In land use and agricultural practices.
- Aerosols due to volcanoes, industrial pollution, dust from the earth, interstellar dust.
- Greenhouse gases.
- Solar emissivity and orbital parameters.
- Polar icecaps and melting of glaciers.
In addition, there are the effects of chaos. In particular, there are effects due to changes in the oceanic circulations - eg El Niño and La Niña which are known to be related to large scale weather patterns. This natural variability can make long-term trends difficult to detect from short records.
From Satellite based temperature records prodided monthly by Spencer and Christy.,
The modellers and the climatological statisticians take a number of important steps. First, they compare the behaviour of their models with what has happened and is happening in the period for which we have good instrumental, meteorological data. In other words do the models describe the weather of the last century reasonably well?
Then the models can be checked against longer period records, mainly of temperature, such as the CET series. The next test is to use the proxy data describing the chemical composition of the atmosphere in previous ages.
These data can be put into the models to see if they are capable of producing reasonable representations of the climate as it was both during man's lifetime and in prehistory.
Weather varies naturally from day to day, month to month, year to year, and on longer time scales. Occasionally this variability leads to extremes of temperature or precipitation. An important test of a climate model is whether it can reproduce, credibly, the observed natural variability. A climate prediction index has been developed by the Hadley Centre as a means of comparing the performance of climate models against a range of different indicators (such as surface temperature, rainfall and surface pressure) using a single number.
In a very specific sense, the models are validated by comparing simulations with events such as the last glacial maximum (the peak of the last ice age, around.21000 BC). Such testing gives confidence in predictions of the global mean temperature rise now expected over the 21st century. This is expected to be in the range 2 - 4.5°C depending on the greenhouse gas emissions assumed by the IPCC.
Taken from the IPCC Panel 1 Assessment Report 5, Chapter 9 (2013), this shows how all the climate models were able to reprsent what actually happened since 1870,
The models can be run with various scenarios and the sensitivity of the climate to different factors estimated. The amounts of carbon dioxide, methane, sulphur dioxide and other gases can be varied and the different responses calculated and compared with observation.
Taken from IPCC Panel 1 Assessment Report 4, Chapter 9 (2007), This shows the results of climate simulations when anthropogenic greenhose gases are not included. The solid black line shows how air temperatures have actually changed since 1900. The blue lines show model simulations with the average shown as a solid blue line.
Other possible impacts can be studied such as the response to solar intensity changes and man made aerosols. Volcanic eruptions can be included and compared with observations after such events.
These effects, generally, are weaker in terms of long term effects and, therefore, more uncertain than those of greenhouse gases. The past 1,000 years are a particularly important time-frame for assessing the background natural variability of the climate. The solar input has remained largely unchanged and the spatial extent of large-scale climate change during the past millennium can now be estimated with some confidence.
From time to time specific reasons are postulated that might explain changes in climate. Changes in the earth;s orbit round the sun, changes in the tilt of the earth, micro-phsical effects and so on can all be tested. So can various scenarios such as zero grwoth in CO2.
One particular theory is due to the Danish space scientist, Svenmark, who suggested that the effects of cosmic rays on clouds could be a significant factor. It should be possible, and may have been done, to test such theories using the omodels.
Results of Models and Other Studies
As noted earlier the slow down in rising sea level temperatures is interesting to climate scientists partly at least in that it calls their results into question. Looking at this problem, The IPCC AR5, WG1, Chapter 9, 2013. used results from 116 ensembles starting in about 1850. They Looked at the overall rise in global temperature anomaly for the period 1951-2012. They then compared tis to the two 15 year periods 1998-2012, the pause period, and 1984-1998 just preceding the pause
The main observational conclusion is that the variations and trends of all the main indicators consistently show an increasing global surface temperature over at least the last century. However, substantial shorter-term global and regional deviations from this warming trend are likely to have occurred
For example, the best estimate of global surface temperature change is a 0.6°C increase since the late 19th century with a 95% probability range of 0.4 to 0.8°C.
It is likely that there have been real differences between the rate of warming over the last twenty years, which are not fully understood. Palaeo-climatological analyses for the last 1,000 years over the Northern Hemisphere indicate that the magnitude of 20th century warming is likely to have been the largest of any century during this period.
At some 18 climate research centres around the world, climate models are run under various assumptions of the chemical composition of the atmosphere. For details of the various centres can be found in the IPCC AR5, WG1, Chapter 9, 2013.
These are three of the scenarios used.
- Rapid economic growth towards a service and information economy.
- Population rising to 9 billion in 2050 and then declining.
- Reductions in material intensity and the introduction of clean and resource efficient technologies.
- An emphasis on global solutions to economic, social and environmental stability.
- A world of independently operating, self-reliant nations.
- Continuously increasing population.
* Regionally oriented economic development.
- Slower and more fragmented technological changes and improvements to per capita income.
- Rapid economic growth.
- A global population that reaches 9 billion in 2050 and then gradually declines.
- The quick spread of new and efficient technologies.
- A convergent world - income and way of life converge between regions.
- Extensive social and cultural interactions worldwide.
- A balanced emphasis on all energy sources.
These scenarios are shown here with these predictions.
This shows the outcomes for the three scenarios above together with what would happen if CO2 levels remained constant. Rhe shaded areas around each cyrve indicate levels of uncertainty.
The Hadley Centre has examined the causes of 20th century temperature change on the continental scale. Here, the focus is on the land masses of North America, Asia, South America, Africa, Australia and Europe.
The modelling study investigated the historic impact on the climate system of greenhouse gases alone; the combined effect of sulphate aerosol, lower atmosphere and stratospheric ozone; the combined effect of volcanoes and changes in the output of the sun.
It should be noted that the sea level is expected to continue to rise beyond this period. On this time scale the major component of the sea-level rise is the thermal expansion of the oceans. Because the oceans have a large thermal capacity they take a long time to adjust to changes in atmospheric greenhouse gas concentrations, and the effects on future sea-level rise beyond 2100 (expressed as a percentage of the 21st century rise) is much greater than the effects on temperature rise. Observations of temperature show that there have been large regional variations in the amount of warming.
Whether or not man is responsible for climate change, the question that sailors will be concerned with is what is happening to sailing weather. Measurements from a number of sites across the United Kingdom and Iceland show that the occurrence of deep depressions, which can cause severe impacts, has changed over recent times. However, this storm record is not long enough to determine whether this represents a long-term trend.
Hadley Centre scientists have studied changes in storm characteristics over the past 50 years or so. The average number of storms shows a significant increase in the United Kingdom winter period (October to March). Regional analysis shows that the largest increases occur over the southern UK. Iceland has experienced a slight reduction in the number of storms (between October and November), although this reduction can not be separated from natural variability with any degree of certainty.
A reduction in storm frequency in the north and an increase in the south is consistent with a southerly movement of the North Atlantic storm track. The severe storms over the UK are more related to strong local gradients of pressure than to the large-scale pressure differences over the Atlantic. One effect that may be starting to become noticeable is the length of the hurricane season. Hurricanes need, among other things, sea temperatures over large areas of at least 26 C. A warming of the seas on the large scale might mean an extension of the season. The 2003 hurricane season started around 22 April while normally, hurricanes are expected from June onwards.
Another indication of possible global warming effects is the hurricane seen here to be forming over the South Atlantic on 26th March, 2004. This is the first hurricane ever reported over that ocean. Conventional wisdom is that the seas are just not warm enough. It would be facile to say that this is definite proof of global warming. But, it is just another abnormal occurrence that lends credence to the concept.
It is important to place these results into context. Evidence of storm frequency from daily indices and measurements of wave heights suggest that although it has increased in recent times, the magnitude of storminess at the end of the 20th century was similar to that at the start. This could mean that natural variations in the magnitude of storminess on time scales of several decades or more are responsible for all or part of the trends seen in these new results and that data covering a longer period are needed in order to distinguish a climate change trend from the natural variability.
Climatological statistics have their uncertainties as does climate modelling. Nevertheless, the results of the best work so far done is worrying, to say the least. It is not at all clear whether there is much that man can do to reverse the trend to any significant extent in the short term.
There are many ways of reducing dependency on fossil fuels and, at some stage in the future, fossil fuels will run out. In any case, they will become increasingly costly to extract. None of us likes large wind farms. Solar energy has much to commend it but is not too reliable in the UK, for example.
Wave or swell seem useful and very green but will be costly to harness. Tidal barrages, again, are very green but are not to everyone's taste. Fuel cells have promise. Hydro-electric is very green but only available in selected areas. It is just possible that implementing some or all of these will reduce the effects and in the very long run, even reverse them.
This is not the forum to indulge in political discussion or to pontificate on what man should do collectively. It may or may not be too late to do anything to change the trends in any significant way in the lifetime of our children or grandchildren.
The bottom line
The question that the politicians have to ask themselves is "Can we afford to ignore the warnings from the experts and continue to do little or nothing to try to ameliorate what seem to be the logical outcome of the current observed effects?" But, implementation of many sources of green energy will mean that many of us will have to accept unpalatable solutions. Do we have the strength of character to accept restrictions to our personal freedom and reductions in our quality of life for the sake of future generations?
The experts might just be wrong; can we take the chance
Answers on a postcard, please!
Postscript - Over simplification!
My suggestion that warmer oceans will make hurricanes and typhoons more frequent may be an example of the danger or over simplification. This is a hazard in meteorology. Nothing is simple. Some recent research has suggested that a consequence of warmer oceans may be greater wind shear in the vertical. Tropical storm formation can be inhibited by large wind shear.
So, although the suggestion of increased hurricane activity may sound reasonable it may not, in fact, occur. However, one might very reasonably expect those hurricanes that do form to be more intense because of the greater potential for energy from the condensation of water from warmer waters.. it is just that there not be an increase ion number.
This article was written for Cruising, the quarterly magazine of the Cruising Association. I have tried to give as balanced account of Climate change as is possible for a (former) professional meteorologist. There are many wild and misleading statements made about the reasons for the current climate change. I have taken the view that only statements made by reputable scientists and subject to peer review in the open literature are worthy of consideration.