Climate Change - Fact or Fiction?

Meteorology is a very broad subject and I should like to make it quite clear that 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, some of whom are still involved. This article has been produced partly, and unashamedly, using output from the Hadley Centre for Climate Prediction and Research, now regarded as a world leader on this most important topic. Other sources were the IPCC (International Panel on Climate Change) and websites of organisations that contributed to the IPCC Assessment Reports of Working group 1, the Scientific Panel.

Significant advances in meteorology require the largest computers available. Current computers used have speeds of around 1015 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 . That means that the major centres capable of undertaking climate research have to be funded by governments. In the IPCC Panel 1 latest report, AR4, there are some 18 centres listed. These are the main sources of assessments of climate change although there are many university departments capable of assessing and criticising the science and its application. It follows that the results quoted below have all been subjected to critical peer review.

Is climate changing? The answer must always be "Yes". Climate has always been changing. But, the question then becomes "Are the current changes really unusIs climate changing? The answer must always be "Yes". Climate has always been changing. But, the question then becomes "Are the current changes really unusual?" and "Is man to blame?" Like so often in meteorology, this simple question is extremely complex.

Early attempts to determine the role of man in causing climate change used temperature observations and related these statistically to the use of fossil fuels. The qualitative argument is that short wave radiation from the sun passes through the atmosphere (as it does through a glass window) and heats the earth which, in turn, warms the atmosphere.

An important question is, “Can those qualitative arguments stand up when examined rigorously?”

This is necessary if findings, which may be unpalatable to some, are to carry weight and lead to action, if possible. In other words, theories of the physical and chemical processes of the atmosphere should be scientifically sustainable. In effect, can the science really account for the observed changes and can they help to predict the future?

Conversely, arguments that deny such man-made effects should also be able to withstand scientific scrutiny.

Those seriously in the business of climate change, such as the scientists at the Hadley Centre and, more generally, those contributing to the IPCC Scientific Assessment reports, would 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 by conduction leading to convection, by radiation and through latent heat when water freezes/melts or condenses/evaporates. These processes depend upon the nature of the ground, its orientation, vegetation, land use etc. Mankind can affect some of these.

Little of the sun’s incoming radiation heats the air. Most of the heating comes from the absorbtion of outgoing infrared radiation by gases, primarily water vapour, CO², CH⁴ , various industrial gases and ozone. There are aerosols that come naturally from volcanoes, from dry land and outer space. Man can both affect some of these natural processes add to them. Aerosols can absorb infrared and emit infrared radiation but, overall, have a cooling effect.

On timescales of varying lengths, heat input from the sun can change. This can be due to variation in emissivity eg sunspots, variations in the tilt of the earth and in its orbit round the sun.

The net effect is that the earth’s climate is continually changing for two main reasons. First, there are the external factors such as greenhouse gases, changes in solar output, volcanoes, interstellar dust and man-generated aerosols. Then there are natural) fluctuations in the climate. These can be large enough to cause apparent increases, decreases or even reversals in long term trends.

This is well shown here -

There is an obvious upward trend in geenhouse gases but the rise in global temperatures is much more variable. This leads to understandable doubts and is a fact used by those that doubt that man is affecting the climate. It is easy to select a short period as shown here

to "prove" that man is not having any effect on the climate.'''

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 and some of the longest near homogeneous records (dating back to the 17^th century) are from Central England (the 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 maintains this quasi-homogeneous record.

See the Hadley centre site for details

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 effect 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, and observing practices have changed. 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. These data, combined with satellite measurements of sea temperature, have been used to derive a graph of changes in sea surface temperature since the start of the data series.

Studies such as this show a warming which could be within the normal noise level of climate variability. The period is too short to make any scientifically defensible deductions about the long term trends. Although they confirm the concept of global warming they might just be showing a large, long period oscillation.

There are measurements of atmospheric concentrations of CO² such as that here produced by the NOAA NCDC.

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, from AD 900 to 2004, The figure is from a report of The Intergovernmental Panel on Climate Change (IPCC). It shows hoe climate has changed over different areas.

Source IPCC AR4 Chapter 6..

There is good factual evidence that the 20th century warming trend is continuing. The average global temperature over land in 2002 was around 1 °C warmer than at the end of the 19th century. 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.

A NOAA?NCDC Temperature change and carbon dioxide change

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 earthm 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. These natural can make long-term trends difficult to detect from short records.

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.

See the NOAA site for more details.

Taken from the IPCC Panel 1 Assessment Report 4, Chapter 8 (2007), this shw#ows how all the climate models were able to reprsent what actually happened since 1900,

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 simulations for the same period when the effects of anthropegenically produced greenhouses gases are rmoved.

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.

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 Panel 1 Assessment Report 4,chapter 8.

These are three of the scenarios used.

B1

• 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.

A2

• 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.

A1B

• 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.

Regional effects

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.

Sea levels

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 26^th 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 if 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.

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.