Why the fuss?
Lets start by taking a look at the annual global surface temperatures since the seventies. Prior to this period ups and downs were more even. The graph below shows the temperature relative to the pre-industrial average based on 1850 to 1900. The Paris agreement was to maintain the temperature significantly below a 2 degree C increase. By which 1.5oC has been the aim. In 2024 the one year average rose above 1.5oC. However it can be seen from the graph that the natural variations we have been seeing would be expected to drop the one year average below 1.5 for the next few years. The rolling averages of the previous 5 and 10 years are also shown on the graph. If the temperatures were stable we would expect there to be an almost equal number of yearly temperatures (blue dots) above and below these lines. So it is clear that the temperatures have been rising and from the trends one could expect both 5 and 10 year average to rise above a 1.5oC increase sometime around 2030.
The Paris agreement aimed for NET zero in 2050, but, many countries are not even aiming for that. Those that are, are having difficulty with rich and powerful lobbies demanding the right to continue polluting our atmosphere. Thus, it is evident that the 1.5oC target is no longer realistic. The 2Oc target is more plausible but realistically is unlikely to be kept to.
Lets have a look at the average temperature in England over a 5 or 10 year period and see how that has altered over the past 100 years or so. This way we avoid the confusion of single year variations and get a better picture of trends. Being a smaller part of the planet the variations seen are larger than for the global average. The trends seen are similar with not much to show prior to the 80s and then a definite warming effect. It also shows how the average in part of the world can go down, even when the global average is going up. The effects of cycles in air and ocean currents will continue to give rise to these localised drops in temperature even with a longer term increase. If a tipping point is traversed in one of the planets circulatory systems that caused longer term changes you would need 20 to 30 years to confirm such a change from average temperature data unless the change made a very drastic, fast and permanent change.
Global and Local Temperatures
Global and local temperatures vary naturally. Taking averages over wide areas, such as the entire globe reduce but does not eliminate natural variations. Causes include:
- Day length.
- The unequal split of land and sea between northern and southern hemispheres.
- Distance to the sun (Earth's orbit is an ellipse not a circle).
- Volcanic activity.
- Amount of our planet covered in ice.
- Make up of the atmosphere.
- Amount and type of cloud.
- Cycles in the Sun's activity.
Historical evidence: Global temperatures can be tracked back through history along with make up of the atmosphere and even amount of plant and animal life and the existence of ocean currents, by looking at ice, earth, and rock samples from around the globe.
It has long been established that there have been intermittent catastrophic events causing widespread species extinction. The existence of recent Ice age events is also well established from records and the temperatures and atmospheric components from these eras are now well known.
Predicting Temperatures: Global temperature models have now become accurate enough to be able to predict backwards in time to predict the temperature variations seen in the records.
To predict the temperatures and the rapid changes in global temperatures that we have seen in the last century the global temperature models have to include the effects of man made pollution to the environment.
Predicting into the future can be performed relatively accurately using the calibration of the models when backtracking into our history. There are some significant unknowns going forward, the most significant being just how much more greenhouse gases are humans going to add to the atmosphere.
Scientists build models of the features important in determining the planets temperature to do this.
Global models: Simplistically the heat energy of the world tomorrow is today's heat energy plus the heat energy received from the Sun minus the heat energy emitted by the earth into space. As the earth is essentially contained within the vacuum of space the energy is effectively received and emitted in the form of radiation and not conduction (we cannot touch the sun) nor convection (insufficient material density for material flow).
Radiation: We are familiar with how the sun's radiation causes us to warm up when we sit in the sun on a sunny day. All items radiate heat but hotter items radiate heat at higher "energy levels". Again we are familiar with this when we are heated up by the sun's radiation but trap the lower energy radiation within a greenhouse or conservatory. We also know from sitting in the shade that the radiation can be blocked from hitting us by something between us and the sun (a tree, a building or a cloud maybe) and either reflects the radiation or absorbs it itself. Note how black steering wheels get scoldingly hot on sunny days. This is like the dark oceans and land masses heating up in the sun whereas white snow covered land reflects the sun and does not warm up so much. Clouds both stop heat escaping at night keeping the temperature up and also block and reflect during the day so keeping the temperature low, clouds at different levels have different effects.
Balance: Once the surface of the earth is hot enough for the emitted radiation to equal the absorbed radiation from the sun the earth will stop getting hotter. We can see from above however that:
1 If we have less white ICE the planet will absorb more heat rather than reflect it. This results in the input energy going up so to keep a balance the output energy will need to go up as well. We can do this by allowing the planet to warm or by removing the glass in the "greenhouse" so as not to trap the energy in the first place.
2 If we make the glass on our greenhouse better insulating we will need to make our greenhouse hotter to allow the emitted radiation to escape and balance the incoming radiation. Although if we shade the greenhouse it will not get so hot (receive so much input heat) so can balance at a lower temperature. If we heat our greenhouse then this extra heat is like extra sun and the greenhouse will get hotter before it reaches a balance of in and out energy.
3 Clouds can both cool and warm the earth.
Convection and conduction: Whereas the heat into and out of the planet is basically radiation based within the planet itself both convection and conduction play their parts. If extra heat coming into the planet were buried deep within the oceans or deep down in the earths crust the surface would not necessarily warm up, or warm up more slowly. A natural example is the southern ocean currents known as El Nino and La Nina, in one state the warm surface water is buried deep in the oceans, so cooling the surface, in the other warm water is returned to the surface so warming the surface. It is the surface layers that radiate to space and in which we and many of earth's lifeforms live. On land conduction of the heated surface downwards causes permafrost to melt. This melting shows that the surface is getting warmer, but also absorbs energy to change the state of the water from ice to water without changing the temperature. Unfortunately rather than slow temperature rise methane and other greenhouse gasses are released when permafrost thaws, so adding to the problems.
Variations in heating the Oceans and the atmosphere cause differential pressures owing to expansion of warmer fluids, add in the rotation of the earth and friction and currents are set up in both oceans and atmosphere.
Other energy forms: When ice melts the energy is absorbed without raising the surface temperature, however once melted the now grey land or sea will not only get hotter from the energy that previously melted the ice but will also absorb more energy owing to absorbing more and reflecting less radiation, a double whammy.
The energy in the light radiation from the sun can also be turned into chemical energy, trapped through processes, such as photosynthesis. Conversely this energy can be released back through process such as animal respiration and burning fossil fuels, though the big hit with these is the CO2 production which acts as an insulator (greenhouse gas).
So where are we today? Today (end 2024) the global surface temperature is approximately 1.6oC above pre-industrialised levels. This is an average, normally as land warms faster than the sea the land will have warmed by more than this amount and the sea, on average less. The extremes of high and low temperatures have also increased in many parts of the world beyond this value.
Is this forever? Probably not in the short term. Natural cycles such as the famous El Nino/ La Nina events bury heat down into the ocean depths and then bring it back to the surface again. This is one of the causes of the variations we see in global average temperatures and is expected to lower the global temperature in the short term, having just raised the temperature during 2023 and 2024. C3S are expecting the underlying global temperature (as against an individual year such as 2024) to rise above 1.5 degrees around about 2030 and report individual years prior to then could reach 1.9 degrees above pre-industrial levels. In the longer term it is believed that the current CO2 concentrations dictate an average temperature above 1.5oc above pre-industrial era. These concentration levels are still going up which means a higher temperature to reach an energy balance for our planet.
Is this the same everywhere on the planet? No, not all areas of the planet are heating up equally. Some areas are heating up more than other areas and there is one area in the north Atlantic which has been cooling. This varied heating is predicted in global temperature models but the exact details are in some areas lacking in clarity and further work is needed to improve knowledge.
What does this imply for Knebworth? So far Knebworth has been only lightly effected with a modest rise in average temperature but with worse temperature extremes. The average temperature in England for the period 1991 to 2020 was approximately 1 degree C higher than the average during the period 1961 to 1990. Looking forward the general warming effect on the globe results in higher moisture content so more severe storms. Weather events are expected to be more severe and hang around for longer, so dry spells could last longer. Winter storms may not just contain heavier rain and stronger winds but are also likely to take longer to pass over so making them even more lethal, even if total annual rainfall remains much as it is today (Rainfall has actually risen which may be expected as hotter air is able to absorb more water.). The last UN report (6) showed diseases such as malaria spreading to Calais and possibly also into Kent as a result of the climate changing so that tropical diseases could survive much closer to home than currently is the case.
Could Knebworth actually get colder? At the time of the latest UN report the North Atlantic meridional overturning currents were not thought to be in danger of ceasing this century, since then measurements and further research has resulted in the scenario being taken much more seriously. Looking back into the past it can be seen that gulf stream warming effect has turned off on several occasions. Importantly in the past there were no man made effects forcing changes much faster than is in records, and potentially changing the manner of the natural interactions between air current circulations, water current circulations, melt water volumes and coastal geometries. All of these have degrees of uncertainty that make it very difficult for scientists to predict exactly and also to get the timescales over which the changes occur. It is possible that the AMOC may take decades to slow down but it could kick start again very quickly.
How AMOC failure effect Knebworth, if it happened? The potential effects on Knebworth's temperatures are not clear. Reports indicate possible temperature reductions of up to 15C in parts of NW Europe for AMOC collapse, for Knebworth probably not so bad, just 3 to 5 degrees C down. A decent prediction for global warming plus AMOC failure has not been found. That said the effects of AMOC failure on Scotland appear to imply significant crop failure, which would clearly have implications for Knebworth. We may be hungry.
What does this all mean?
- The goal of keeping the rise in human caused temperature increase to significantly less than 2oC (by which is meant 1.5oC) is not yet theoretically dead as this implies that the long term average (at least a decade, not actually defined, frequently taken as a 20 year running average) is above 1.5oC. As of Feb 2025 the period over which the average is over a 1.5oC rise is 2 years.
- Natural variation in global temperature is likely to drop the average global temperature below 1.5 in the near future. (if it does not this would be very bad news) However as human activity is still increasing the greenhouse gas concentration the likelihood of keeping below 1.5 is now realistically dead.
- Current trends in emissions would suggest a human induced rise more like 8 degrees but if promised reductions do actually take place a 3 degree rise is perhaps realistic. Keeping below a 2 degree rise is potentially possible but for this drastic action needs to be taken, lead by developed nations. Some developed nations have plans to tackle the easiest forms of carbon emissions to remove but are still expanding emissions in areas such as flying which is mainly driven by the richest segment of all nations developed or undeveloped. Some developed nations are maximising the profits the fossil fuel companies make, which also benefits mostly the richest part of society whilst the consequences can be least well coped with by the poorest.
- It is very much still worthwhile endeavouring to keep the human induced rise below 2 degrees. With these changes occurring in such a short timescale nature and we will find the cost of adaption much more difficult to cope with than a slower change. Once we exceed a 2 degree rise from pre-industrial we are very much in uncharted territory and the chance we hit a tipping point from which we cannot recover ever increases. As temperatures rise so larger amounts of the globe will become effectively uninhabitable, either by heat or flood, with further temperature rises forcing migration to cooler parts of the planet which remain above sea level. The higher we drive greenhouse gas levels the faster the changes will occur.