Delving a little deep into these figures shows that the Earth ’ randomness land areas were 1.43C warmer than average, while the oceans were 0.77C ardent. This is evidence of how the universe ’ s continents have warmed more quickly than its oceans over late decades .
This line between bring and ocean temperature change will strongly shape the ball-shaped traffic pattern of future calefacient and has significant implications for humans. We are, after all, a species that much prefers to live on land .
But what drives this warming contrast ? It ’ s a deceptively bare question, but one with a much-misunderstood answer. In this guest post, I outline a robust, quantitative hypothesis for the land-ocean thaw contrast that has lone been developed in holocene years.
Heat capacity
bare physics suggests that when you put more heat into the climate system, land should warm more promptly than oceans. This is because country has a smaller “ estrus capability ” than water, which means it needs less heat to raise its temperature .
The chart below shows how the Earth ’ mho land open ( yellow line ) has warmed more quickly than the ocean ( dark blasphemous ) over the experimental record .
Amplified warming over land evident in surface temperature records from NOAA. Chart shows annual average temperatures for land (yellow line), ocean (dark blue) and land and ocean combined (light blue). All figures relative to 1901-2000. Amplified warming over country apparent in surface temperature records from NOAA. Chart shows annual average temperatures for state ( chicken line ), ocean ( dark blue ) and land and ocean combined ( light aristocratic ). All figures relative to 1901-2000. Data from NOAA ; chart by Carbon Brief using Highcharts This effect can besides be seen in different parts of the seasonal climate arrangement. For example, as the sunlight moves union of the equator during the northern hemisphere give, its department of energy quickly heats India relative to surrounding oceans. This contrast in heating plays a key function in the about-face of winds that drives the South Asia monsoon .
Land ’ s little heat capacitance besides helps to explain why some continental regions, such as Russia and the cardinal US, can get very hot in summer yet bitterly cold in winter. This is known as “ continentality ” .
Given its central function in the seasonal worker land-ocean warming contrast, inflame capacitance is the natural begin point when attempting to explain why continents warm more than oceans under climate change. But there is a problem with this explanation .
Warming contrast
In a landmark 1991 composition, meteorologist Syukuro Manabe and his colleagues used an early climate model to compare the ephemeral response of the climate system to gradual increases in CO2 to the long-run equilibrium response .
In early words, they were comparing the climate while CO2 was increasing with the climate once CO2 had stopped rising and the climate had finally stabilised at its new, affectionate state .
If the deviation in heat capacities between state and oceans was the decisive factor controlling the warming contrast, we would expect the contrast to disappear at chemical equilibrium once the oceans have had sufficient time to warm up .
But this is not what Manabe found. rather, he discovered that the proportion of land to ocean warming ( now known as the “ amplification factor ” ) was similar in both the ephemeral and equilibrium experiments .
This was attest that the land-ocean heating contrast – highlighted in the map below of project warming for the end of this hundred – is a fundamental response to climate change that is not controlled by heat capacity. If heat capacity can not explain inflate land warming in a change climate, what can ?
Beyond heat capacity
The first base explanation, initially put ahead by Manabe, invokes the surface energy balance. This describes the exchange of energy between the Earth ’ s surface and the atmosphere above it .
When atmospheric CO2 concentrations increase, radiotherapy into Earth ’ s surface increases causing temperatures to rise. This is because a larger sum of the heat radiated by the Earth ’ south surface is being trapped by greenhouse gases in the atmosphere .
But the extent of this CO2-induced coat warming depends on how much is balanced by set factors that cause cooling – namely, cooling caused by vaporization and cooling ascribable to the exchange of dry estrus between the state surface and the air above it. ( The atmospheric warming caused by the latter besides tends to inhibit cloud formation and, frankincense, can cause far dry of the land open. )
Oceans – which have outright water to evaporate – can efficiently cool themselves in a warming climate by evaporating more and more water with only a small temperature increase. Continents, on the other hand, typically have limited moisture handiness and therefore dehydration is constrained .
This means that, over continents, more of the extra radiation going into the coat in a warming climate needs to be dissipated through the exchange of dry hotness and longwave radiative cool, rather than evapotranspiration. This implies a larger increase in surface temperature compared to the freely evaporate oceans .
This “ surface energy balance ” theory for the land-ocean thaw contrast has besides been put forward in more holocene studies .
This explanation for amplify continental warm is intuitive and hints at a key role for estate “ dryness ” in determining the temperature change. But it needs to be supported by heavily numbers .
An issue with the surface energy balance theory is that it relies on properties of the bring surface – which are varied, building complex and notoriously unmanageable to simulate – in order to be accurately represented in climate models. In detail, quantifying how evapotranspiration will respond to a changing climate – the key component of the come on energy balance theory – requires cognition of regional soil moisture and vegetation and how these properties themselves change with climate. A difficult undertaking.
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furthermore, factors in the overlying atmosphere are besides important : how will rainfall and winds change ? The ten thousand processes influencing land surface energy balance beggarly that using this framework as a basis for a quantitative theory for the land-ocean warm contrast is challenging. Although the position is conceptually useful, it provides an incomplete understand of the physics driving the warming contrast .
A new idea
rather than surface energy balance, atmospheric dynamics – the motion of the atmosphere and its thermodynamic express – underpin a modern understand of the land-ocean warm contrast that has developed over the last ten .
In a 2008 paper, Prof Manoj Joshi – then at the Met Office Hadley Centre and the University of Reading and now at the University of East Anglia – was the first to point out that dynamic processes in the standard atmosphere connect temperature and humidity over kingdom and ocean regions .
specifically, he showed that the relapse rate – the rate of decrease of temperature with height – decreases more strongly over ocean than all over land as climate warms. This is because the air above the ocean is, at any here and now in time, typically holding more water vapor than the air over domain .
These contrasting elapse rate changes explain the warming contrast : a weaker decrease in bring elapse rate implies a larger increase in land surface temperature proportional to the ocean .
This mechanism is not necessarily intuitive, but relies on well-established processes in atmospheric dynamics. Differing elapse rate changes are now accepted as the fundamental driver of the land-ocean warm contrast, particularly at low latitudes ( up to approximately 40N and 40S ). Amplified warming in regions including the Mediterranean are besides explained by the same lapse-rate mechanism .
A quantitative theory
With his 2008 wallpaper, Joshi introduced a new conceptual sympathize for the land-ocean warm contrast. But, again, the explanation was qualitative .
together with Prof Paul O ’ Gorman from the Massachusetts Institute of Technology, I realised that the lapse rate argument could be extended and developed into a quantitative theory .
The key insight was that although changes in temperature and humidity over kingdom and ocean are very different, the atmospheric dynamics constraints identified by Joshi imply that changes in a particular combination of temperature and humidity – specifically, the energy contained in a parcel of air travel at lie, a quantity known as damp static energy – are approximately equal. This insight allowed us to derive an equation for the land temperature change, which we published in 2018 .
What our equation shows is that the response of country temperature to climate variety depends on two factors : ocean warm and how dry the down is in today ’ s climate .
The dry the farming is, the more it warms. The theory has been verified in climate models and using experimental data over the past 40 years. The hypothesis explains why land warm is expected to be particularly dangerous in dry, arid subtropical regions and besides explains why relative humidity over nation has been decreasing over late decades .
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An significant implication of the theory for projections of future land temperatures ( which vary well across models ) is that it is crucial to accurately model how dry land is in the current climate, but this is technically slippery due to the complexities of land surfaces .
Not well known
This new reason of the land-ocean thaw contrast has been well received by the atmospheric dynamics and climate dynamics inquiry communities .
But it would be honest to say that it is still not well known in the broader climate science and climate impacts communities that the land-ocean warm contrast is driven by sobriety rather than differences in hotness capacitance .
And it is surely not well known in the populace sector. In terms of the theory itself, some researchers find it surprise that the complexity of land surfaces can be subsumed into a single “ dispassion ” parameter.
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I besides find it surprising and inspiring that the response of a system a complex as continental climate can be boiled down to a simple equation. I would advocate for more of this kind of conceptual inquiry in climate skill .
Sharelines from this history
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Guest post : Why does country warm up faster than the oceans ?
