Dr Michael Byrne, a lecturer in planet surface processes at the university of St Andrews and a Marie Skłodowska-Curie research fellow in the Atmospheric, Oceanic and also Planetary Physics team at the university of Oxford

Last year, worldwide temperatures to be 0.95C warmer 보다 the 20th century average. Human activity is responsible for around 100% that this warming.

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Delving a small deeper right into these figures shows the the earth’s land areas were 1.43C warmer than average, while the seas were 0.77C warmer. This is evidence of just how the world’s continents have actually warmed more rapidly 보다 its seas over current decades.

This contrast between land and ocean temperature readjust will strongly shape the an international pattern of future warming and also has crucial implications because that humans. We are, after ~ all, a species that much prefers come live ~ above land.

But what drives this warming contrast? it’s a deceptively straightforward question, however one v a much-misunderstood answer. In this guest post, I summary a robust, quantitative concept for the land-ocean warming comparison that has actually only been occurred in current years.

Heat capacity

Simple physics says that when you put an ext heat into the climate system, land must warm much more quickly than oceans. This is because land has actually a smaller sized “heat capacity” 보다 water, which means it needs less warm to advanced its temperature.

The chart below shows just how the earth land surface (yellow line) has actually warmed an ext rapidly 보다 the s (dark blue) end the observational record.

Amplified warming end land obvious in surface temperature documents from NOAA. Chart shows annual average temperatures for land (yellow line), ocean (dark blue) and land and ocean merged (light blue). All numbers relative come 1901-2000. Data indigenous NOAA; chart by Carbon short using Highcharts.

This effect can also be viewed in various parts the the seasonal climate system. Because that example, together the sunlight moves phibìc of the equator throughout the northern hemisphere spring, its energy rapidly heats India loved one to surrounding oceans. This contrast in heater plays a crucial role in the reversal the winds the drives the south Asia monsoon.

Land’s little heat capacity additionally helps to define why part continental regions, such as Russia and also the main US, can get really hot in summer yet bitterly cold in winter. This is known as “continentality”.

Given its central role in the seasonal land-ocean warming contrast, heat capacity is the natural starting point when attempting to describe why continent warm an ext than oceans under climate change. But there is a difficulty with this explanation.

Warming contrast

In a landmark 1991 paper, meteorologist Syukuro Manabe and his colleagues used very early climate design to to compare the transient response of the climate device to steady increases in CO2 to the irreversible equilibrium response.

In various other words, they were comparing the climate when CO2 was raising with the climate as soon as CO2 had actually stopped rising and also the climate had eventually stabilised at its new, warmer state.

If the difference in heat capacities between land and also oceans was the decisive factor controlling the warming contrast, we would suppose the contrast to disappear at equilibrium once the oceans have actually had adequate time to heat up.

But this is not what Manabe found. Instead, he found that the ratio of floor to s warming (now well-known as the “amplification factor”) was similar in both the transient and also equilibrium experiments.

This was evidence that the land-ocean warming contrast – highlighted in the map below of projected warming because that the end of this century – is a basic response to climate adjust that is not controlled by warm capacity. If warmth capacity cannot explain enhanced land warming in a changing climate, what can?


Climate model projection of the readjust in near-surface temperature by the end of the 21st century (2080-2100) loved one to the historical period (1980-2000). Data native the GFDL-CM4 version under the fossil-fueled, high emissions SSP58.5 scenario; graph by M Byrne.

Beyond warm capacity

The an initial explanation, at first put front by Manabe, invokes the surface power balance. This defines the exchange that energy between the earth surface and also the atmosphere above it.

When atmospheric CO2 concentrations increase, radiation right into Earth’s surface increases causing temperatures to rise. This is due to the fact that a larger amount of the heat radiated by the Earth’s surface ar is gift trapped by greenhouse gases in the atmosphere.

But the degree of this CO2-induced surface warming depends on exactly how much is balanced by localised components that cause cooling – namely, cooling resulted in by evaporation and cooling because of the exchange of dry heat in between the floor surface and also the air over it. (The atmospheric warming led to by the latter additionally tends to inhibit cloud formation and, thus, can reason further drying of the land surface.)

Oceans – i beg your pardon have countless water come evaporate – can effectively cool us in a warming climate by evaporating much more and more water with just a small temperature increase. Continents, on the other hand, frequently have limited moisture accessibility and so evaporation is constrained.

This method that, over continents, much more of the extra radiation going into the surface ar in a warming climate requirements to be dissipated with the exchange of dried heat and longwave radiative cooling, fairly than evapotranspiration. This implies a larger rise in surface ar temperature contrasted to the openly evaporating oceans.

This “surface energy balance” theory for the land-ocean warming contrast has additionally been put forward in much more recent studies.

This explanation for magnified continental warming is intuitive and hints in ~ a an essential role for land “dryness” in identify the temperature change. However it requirements to be sustained by tough numbers.

An issue with the surface energy balance concept is that it relies on properties of the land surface – which space varied, complex and notoriously complicated to simulate – in bespeak to it is in accurately stood for in climate models. In particular, quantifying just how evapotranspiration will certainly respond to a changing climate – the vital ingredient that the surface energy balance concept – requires expertise of local soil moisture and vegetation and how these properties themselves adjust with climate. A complicated task.

Moreover, components in the overlying setting are additionally important: exactly how will rainfall and winds change? The myriad processes influencing land surface power balance median that using this framework as a basis for a quantitative theory for the land-ocean warming comparison is challenging. Although the view is conceptually useful, it offers an incomplete knowledge of the physics control the warming contrast.

A new idea

Rather 보다 surface power balance, atmospheric dynamics – the activity of the atmosphere and also its thermodynamic state – underpin a new understanding the the land-ocean warming comparison that has developed over the last decade.

In a 2008 paper, Prof Manoj Joshi – climate at the Met Office Hadley Centre and also the college of Reading and now in ~ the college of east Anglia – was the very first to suggest out that dynamical procedures in the atmosphere affix temperature and humidity over land and also ocean regions.

Specifically, he showed that the lapse price – the rate of to decrease of temperature with height – decreases an ext strongly over s than over land together climate warms. This is due to the fact that the air over the s is, at any type of moment in time, frequently holding an ext water vapour than the air end land.

These contrasting lapse rate alters explain the warming contrast: a weaker to decrease in land lapse rate means a larger increase in land surface ar temperature relative to the ocean.

This system is not necessarily intuitive, yet relies top top well-established procedures in atmospheric dynamics. Differing lapse rate changes are now embraced as the an essential driver of the land-ocean warming contrast, particularly at short latitudes (up to roughly 40N and also 40S). Amplified warming in regions including the Mediterranean are additionally explained by the exact same lapse-rate mechanism.

A quantitative theory

With his 2008 paper, Joshi presented a new theoretical understanding because that the land-ocean warming contrast. But, again, the explanation to be qualitative.

Together with Prof Paul O’Gorman native the Massachusetts academy of Technology, i realised the the lapse rate argument can be extended and developed right into a quantitative theory.

The an essential insight was that although changes in temperature and humidity end land and also ocean are an extremely different, the atmospheric dynamics constraints determined by Joshi imply that alters in a particular combination of temperature and humidity – special, the energy consisted of in a thoreau of air at rest, a quantity recognized as moist static energy – are approximately equal. This insight permitted us to have an equation for the soil temperature change, i beg your pardon we published in 2018.

What our equation reflects is that the response of land temperature to climate adjust depends on two factors: s warming and how dry the floor is in today’s climate.

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The drier the floor is, the an ext it warms. The theory has actually been verified in climate models and also using observational data end the past 40 years. The theory defines why soil warming is expected to be particularly severe in dry, arid subtropical areas and additionally explains why relative humidity end land has actually been decreasing over current decades.