Corlett r 20150708_1500_upmc_jussieu_-_amphi_herpin

No-analogue climate futures

in the tropics

Richard T Corlett

Center for Integrative Conservation

Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, Yunnan

It is getting warmer in the tropics, (0.7-0.8oC since 1950). Much of the variation is associated with ENSO, making 1998 the warmest year so far in much of the tropics. Annual and 5-year running mean land surface temperature from NASA-GISS

Northern

Southern

Tropical

Climate models predict a further 1-2oC warming in the tropics by 2050 and 1-5oC by 2100, depending on assumptions. temperature precipitation

Diffenbaugh & Field 2013 Science

2050 2100

Climate models predict a further 1-2oC warming in the tropics by 2050 and 1-5oC by 2100, depending on assumptions. temperature

Moritz and Agudo (2013) Science

2050 2100

Temperatures in the late 21st century are expected to be the warmest for at least 5 million years, i.e., novel not only for modern species, but also for the lineages they belong to.

Diffenbaugh & Giorgi 2012, Climatic Change

Amazon

West Africa

Indonesia

Qinghai-Tibet Plateau

The climate change hotspots

If the mean, variability and extremes of temperature and precipitation are considered, the greatest climate changes are projected for the tropics:

Fischer & Knutti 2015, Nature Climate Change

Moreover, the probability of hot extremes (> 99th and 99.9th percentile of pre-industrial daily temperature) increases much more rapidly than global mean temperatures. So the probability of a hot extreme with 2oC warming is almost 2X that with 1.5oC (and 5X at 0.85oC) These probabilities will be greatest in the tropics.

Projections for other types of extremes are unclear: Tropical cyclones: models suggest fewer but more intense cyclones. [Kang & Elsner, 2015, Nature C.C.]

Droughts: no strong evidence for any general trend in the tropics [e.g. Greve et al., 2014]. Most tropical droughts associated with ENSO (+/- modulated by PDO and AMO) and this masks general trends. There is also no agreement on trends in ENSO, IOD, PDO, AMO etc.

Predicting responses of human and natural systems to novel climate extremes is inherently difficult: Both human societies and natural systems have an inherent capacity to adjust to climate change.

But projected climate extremes will almost certainly kill more tropical people, directly and indirectly, unless adaptation is taken very seriously, with socially marginalized people at most risk.

Bellard et al., 2012, Ecology Letters

For natural systems, a huge range of +/- adverse impacts has been predicted, and some have been observed already in response to recent changes.

For natural systems, a huge range of +/- adverse impacts has been predicted, and some have been observed already in response to recent changes. But … a lot of impact predictions are based on naïve and oversimplified assumptions.

Bellard et al., 2012, Ecology Letters

Novelty is not new.

The paleoecological record shows that most extant species have survived past climates with no modern analogue.

Climates have fluctuated widely over the last 2 million years yet caused few known extinctions [e.g. Kidwell, 2015, PNAS].

We tend to assume that the distribution of species today reflects their fundamental niche, but it only shows their realized niche under current conditions.

i.e. most species can probably live in at least some climates that they do not occur in today.

We tend to assume that the distribution of species today reflects their fundamental niche, but it only shows their realized niche under current conditions.

i.e. most species can probably live in at least some climates that they do not occur in today.

also supported by evidence from invasive species that occupy ‘novel’ climates not available to them ‘back home’.

How will natural systems in the tropics respond to projected changes in climate? Ecosystems will adjust by changes in the distribution and abundance of species. Diversity should help this. Individual species can:

• acclimate (within an individual's lifetime) • adapt (genetically, over >1 generation) • move (to track favorable climate)

• …or die

Option 1: acclimate, through phenotypic plasticity.

Under-researched so no clear patterns, but appears that acclimation capacity is significant , but limited. [e.g. Overgaard et al., 2011, American Naturalist; Slot et al., 2014, Global Change Biology; Simon et al., 2015, J. Thermal Biology]

Option 2: adapt, through evolutionary change

Again too few studies, but is only an option for short-lived species and the capacity for genetic adaption to novel extremes is limited.

Kaspari et al. 2015, Global Change Biology

In rainforest, 8oC between the hottest and coolest surfaces.

Option 3: move – but how far? Between microhabitats - behavioral adjustment.

Option 3: move – but how far? Between microhabitats - behavioral adjustment. Upslope, along steep altitudinal gradients in temperature (but area declines, eventually to zero). Polewards, but shallow thermal gradients in the tropics mean they may require movements of at least 300 m/year to track projected changes.


2050 2100

It is not just temperature…. But projections for tropical rainfall are still highly model-dependent.


2050 2100

It is not just temperature…. But projections for tropical rainfall are still highly model-dependent. And the projected changes are often within the Holocene range of variation and almost always within the Late Pleistocene range, i.e. not very novel.

And it is not just climate…

Amazonian rainforests

climate



climate

land use

rising CO2 fires

Zhang et al., 2015, Global Change Biology



climate

land use

rising CO2 fires

Zhang et al., 2015, Global Change Biology

This is still hotly debated!

Summary: 1. Current climate extremes kill people and interact

with other human activities to kill wild species. 2. They’ll get worse, particularly in the tropics, and

faster than the Earth warms on average. 3. But only projections for temperature extremes are

robust everywhere. 4. Projected extremes will almost certainly kill more

people, particularly the poor and marginalized. 5. Impacts on natural systems are still really hard to

predict, but we should probably worry most about tropical lowlands and mountain tops.

6. We don’t want this: let’s stop climate change!

Thank you!!

[email protected]

Increasing probability and attributable risk of extremes with warming:

Fischer & Knutti 2015, Nature Climate Change

… or for frogs and lizards.

Microhabitats reduced mean temperature by 1–2 °C and reduced duration of extreme temperature exposure by 14–31 times

Scheffers et al. 2014, Global Change Biology

NOAA-NCEI

Cycles on longer timescale cause further complications

oC

Global mean temperature over 5 million years, showing that: Current temperatures are already warm for the last 3 million

years Predicted future temperatures for this century will be warmer

than any period in the last 5-10 million years.

From Moritz and Agudo (2013) Science

now

Occurrence of 1986-2005 maximum summer temperatures:

Diffenbaugh & Giorgi 2012, Climatic Change

Increase in probability of extremes is biggest in the tropics:

The impacts of global warming have been exacerbated in the tropics by deforestation, since forest has a strong local cooling effect from evapotranspiration. Li et al. 2015, Nature Communications