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


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

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Delving a little deeper right into these numbers shows that the earth land areas were 1.43C warmer 보다 average, while the oceans were 0.77C warmer. This is evidence of just how the world continents have warmed more rapidly 보다 its oceans over current decades.

This contrast in between land and ocean temperature readjust will strongly shape the worldwide pattern of future warming and also has vital implications because that humans. Us are, after all, a species that lot prefers to live ~ above land.

But what cd driver this warming contrast? the a deceptively simple question, yet one v a much-misunderstood answer. In this guest post, I synopsis a robust, quantitative concept for the land-ocean warming contrast that has only been occurred in current years.

Heat capacity

Simple physics says that when you put more heat right into the climate system, land should warm an ext quickly 보다 oceans. This is since land has a smaller “heat capacity” than water, which method it demands less warm to progressive its temperature.

The chart below shows exactly how the earth’s land surface (yellow line) has warmed much more rapidly than the s (dark blue) end the observational record.

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Amplified warming end land obvious in surface temperature records from NOAA. Chart shows annual average temperatures because that land (yellow line), s (dark blue) and land and ocean merged (light blue). All numbers relative come 1901-2000. Data native NOAA; graph by Carbon quick using Highcharts.

This impact can also be viewed in various parts that the seasonal climate system. Because that example, as the sunlight moves north of the equator throughout the north hemisphere spring, its energy rapidly heats India loved one to neighboring oceans. This comparison in heater plays a an essential role in the reversal that winds the drives the southern Asia monsoon.

Land’s little heat capacity likewise helps to describe why some continental regions, such as Russia and the main US, have the right to get an extremely hot in summer however bitterly cold in winter. This is well-known as “continentality”.

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

Warming contrast

In a landmark 1991 paper, meteorologist Syukuro Manabe and also his partner used an early climate design to to compare the transient response of the climate device to progressive increases in CO2 come the irreversible equilibrium response.

In various other words, they to be comparing the climate while CO2 was raising with the climate as soon as CO2 had actually stopped rising and also the climate had eventually stabilised in ~ its new, warmer state.

If the distinction in heat capacities between land and also oceans was the decisive factor regulating the warming contrast, we would intend the comparison to disappear at equilibrium when the oceans have had adequate time to warmth up.

But this is no what Manabe found. Instead, he uncovered that the ratio of floor to ocean warming (now known as the “amplification factor”) was comparable in both the transient and equilibrium experiments.

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


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Climate model projection that the readjust in near-surface temperature by the finish of the 21st century (2080-2100) relative to the historical duration (1980-2000). Data indigenous the GFDL-CM4 version under the fossil-fueled, high emissions SSP58.5 scenario; chart by M Byrne.


Beyond heat capacity

The first explanation, originally put front by Manabe, invokes the surface power balance. This describes the exchange of energy in between the earth’s surface and also the atmosphere above it.

When atmospheric CO2 concentration increase, radiation right into Earth’s surface boosts causing temperatures to rise. This is since a larger amount of the warmth radiated through the Earth’s surface is being trapped through greenhouse gases in the atmosphere.

But the degree of this CO2-induced surface ar warming relies on exactly how much is well balanced by localised factors that cause cooling – namely, cooling led to by evaporation and also cooling due to the exchange of dried heat in between the land surface and also the air over it. (The atmospheric warming resulted in by the latter likewise tends come inhibit cloud formation and, thus, can cause further dry of the soil surface.)

Oceans – i beg your pardon have countless water to evaporate – can effectively cool us in a warming climate by evaporating more and an ext water with just a tiny temperature increase. Continents, on the various other hand, commonly have minimal moisture ease of access and for this reason evaporation is constrained.

This method that, end continents, an ext of the extra radiation going right into the surface ar in a warming climate demands to it is in dissipated v the exchange of dried heat and longwave radiative cooling, rather than evapotranspiration. This indicates a larger rise in surface ar temperature contrasted to the freely evaporating oceans.

This “surface power balance” concept for the land-ocean warming contrast has also been put forward in more recent studies.

This explanation for intensified continental warming is intuitive and also hints in ~ a an essential role for land “dryness” in identify the temperature change. But it demands to be supported by difficult numbers.

An worry with the surface energy balance concept is the it depends on nature of the land surface – which are varied, facility and notoriously daunting to simulate – in order to be accurately represented in climate models. In particular, quantifying how evapotranspiration will respond come a an altering climate – the an essential ingredient of the surface power balance theory – requires knowledge of local soil moisture and vegetation and how this properties themselves change with climate. A complicated task.

Moreover, determinants in the overlying atmosphere are likewise important: just how will rainfall and winds change? The myriad processes affecting land surface energy balance median that using this frame as a basis for a quantitative concept for the land-ocean warming comparison is challenging. Back the view is conceptually useful, it provides an incomplete knowledge of the physics control the warming contrast.

A brand-new idea

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

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

Specifically, he proved that the lapse rate – the price of decrease of temperature with elevation – decreases much more strongly over ocean than end land as climate warms. This is due to the fact that the air above the s is, at any kind of moment in time, generally holding an ext water vapour 보다 the air end land.

These contrasting lapse rate alters explain the warming contrast: a weaker diminish in soil lapse rate implies a larger boost in land surface ar temperature relative to the ocean.

This system is no necessarily intuitive, however relies top top well-established procedures in atmospheric dynamics. Different lapse rate changes are now welcomed as the basic driver the the land-ocean warming contrast, an especially at low latitudes (up to about 40N and 40S). Amplified warming in regions consisting of the Mediterranean are additionally explained by the 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 was qualitative.

Together with Prof Paul O’Gorman indigenous the Massachusetts institute of Technology, ns realised that the lapse rate argument could be extended and also developed into a quantitative theory.

The crucial insight was that although alters in temperature and humidity over land and also ocean are an extremely different, the atmospheric dynamics constraints identified by Joshi indicate that transforms in a particular mix of temperature and also humidity – specifically, the energy had in a thoreau of air at rest, a quantity well-known as moist static energy – are around equal. This insight permitted us to have an equation for the floor temperature change, i beg your pardon we published in 2018.

What ours equation mirrors is that the solution of land temperature come climate readjust depends on two factors: s warming and also how dry the land is in today’s climate.

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The drier the floor is, the more it warms. The theory has been showed in climate models and also using observational data end the past 40 years. The theory defines why soil warming is supposed to be an especially severe in dry, arid subtropical areas and likewise explains why loved one humidity over land has actually been diminish over recent decades.