July was remarkably warm, in fact July’s average temperatures—for both land and sea–were the highest monthly temperatures ever recorded since 1850. This image from NOAA illustrates some of the more noteworthy records set last month.
I should also mention that Berkeley Earth (http://berkeleyearth.org), in their summary of 2018 global temperatures published early this year, estimated that 2019 would “…likely… be warmer than 2018, but unlikely to be warmer than the current record year, 2016. At present it appears that there is roughly a 50% likelihood that 2019 will become the 2nd warmest years since 1850.” As of August 15, they are now predicting a 90% probability of this occurring. This screenshot from Robert Rohde’s (BerkeleyEarth) Twitter feed illustrates long-term weather stations (those with at least 40 years of records) that have reported a daily, monthly or all-time record high temperature from May 1st to July 31st. Looks like a sea of red!
Screenshot, August 19 @RARohde
Some of the
more attention-grabbing aspects of the late July heat wave came from Greenland.
Warm air
masses from Europe arrived over Greenland late in July and early August,
causing record-setting melting across about 90% of the ice sheet during a five-day
event. Melt area reached 154,500 square
miles, 18% larger than the 1988-2017 average. The record warmth established an
all-time high melt event for this monthly period, and total ice mass loss for
2019 is nearly equal to that of 2012, the year of highest loss for the
satellite-era. (National Snow and Ice
Data Center Greenland Today)
It’s not
all about the records!
Considerable
attention has been given to elevated Arctic temperatures, increased ice-sheet
melt and its contributions to sea-level rise, and low seasonal sea-ice coverage, but several
other issues attending warming air and sea temperatures warrant discussion as
well. Over the longer term—decades, not days,
warming temperatures are measurably impacting terrestrial and marine
ecosystems. These “slow” ecosystem
changes aren’t as attention-grabbing as all-time records of high temperature or
ice melt, but are one of the distinguishing characteristics of the Anthropocene.
(see “The Anthropocene” tab on the Home page).
Let’s look at a couple of examples, one from terrestrial ecosystems, and
one from marine ecosystems.
In a July 10 article (Hydrologic Intensity) the authors demonstrate in a more complete fashion than previous work, the linkage between rising air temperatures and acceleration of the hydrological cycle. Their model incorporates both the supply of water (precipitation) and demand (evapotranspiration) between the surface and the atmosphere. Reinforcing other research that suggests hydrologic intensification is occurring, the new research shows “widespread hydrologic intenstification from 1979-2017 across much of the global land surface, which is expected to continue into the future.” The findings add a little more support to the likelihood of a climate future where there is “increased precipitation intensity along with more days with low precipitation.” The temporal and spatial distribution of hydrologic intensification will have important consequences ranging from urban flood control to the management of agroecosystems—an issue of considerable importance as population rises this century.
Marine fisheries are also significant food sources for global populations. In an article published in March (Sciencehttps://science.sciencemag.org/content/363/6430/979) researchers looked at 235 marine fisheries (fish and invertebrates) from 38 ecoregions, representing one-third of reported global catch. They concluded that there has been a statistically significant decline in the maximum sustainable yield of 4.1% from 1930 to 2010 that is linked to warming oceans. Five of the ecoregions had losses of 15 to 35%. The authors conclude that “ocean warming has driven declines in marine fisheries productivity and the potential for sustainable fisheries catches.” These trends are exacerbated by overfishing, but sound management plans incorporating temperature-driven trends have the potential for remediating these changes.
Both examples suggest that temperature-driven changes to key provisioning services of terrestrial and marine ecosystems are of equal importance to the headline-grabbing temperature and ice-melt records of the last month. These changes are “slow-motion” impacts of a warming world; like rising sea-levels, ecosystem changes will have profound impacts, but are invisible over short-term news and policy cycles in which we appear to be ensnared.
The recently (Aug 7) released Special Report on Climate
Change and Land by the IPCC (https://www.ipcc.ch/srccl-report-download-page/)
offers a comprehensive review of the nexus between global warming/climate
change and land use change. As I have already
suggested in the “About this blog,” land use changes are a critical aspect of global
anthropogenic change; i.e. the Anthropocene. The new report stresses how a
changing climate (increased air temperatures, evapotranspiration, altered precipitation
regimes, etc.) impact soils and vegetation.
The latter underlie ecosystem health, including agroecosystems, as well
as intact “undisturbed” terrestrial ecosystems such as rainforests, peatland,
and coastal forests. These are critical
harbors of biodiversity, as well as essential elements in the provision of
ecosystem services upon which human well-being depends, such as carbon
sequestration and clean water.
Land use changes associated with agriculture, forestry, livestock,
road construction, and urbanization degrade these critical services, thereby
threatening our ability to sustainably provide food, fiber and other essential
goods and services to a continually growing, telecoupled global
population. Imprudent and ill-planned
(or adhoc) conversion of various terrestrial ecosystems in pursuit of food,
fiber and mineral resources has led to land degradation, desertification and
biodiversity loss at both a scale and speed that are without precedent.
The report emphasizes the urgent need to rein in these
unsustainable practices in order to both guarantee our ability to provide food
for the world, as well as provide a crucial sink for growing carbon
emissions. According to the report,
reducing forest deforestation and degradation are critical elements in
mitigating green house gas emissions.
Furthermore, transitioning the global population to a much more
plant-based diet from one that is significantly animal-sourced, will reduce
risks from climate change as well as help reduce agricultural
extensification.
Only a wide-ranging and comprehensive approach to managing both our energy and land resources will provide sustainable, equitable and healthy outcomes for the global population. Immediate steps need to be taken, because the longer business as usual behaviors continue, our ability to deploy a wide variety of remedies will be increasingly foreclosed. Reducing green house emissions and altering detrimental land use practices are thus interconnected, inseparable and our failure to change both may lead to both irremediable impacts to ecosystems and the goods and services upon which humanity relies.
Rate and Scope of Extinction Source: (“Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services” published in draft form 29 May 2019.) Summary for Policymakers-Advance Draft
The global rate of species extinction is already at least tens to
hundreds of times higher than the average rate over the past 10 million years
and is accelerating (established but incomplete) {2.2.5.2.4}
Human actions
have already driven at least 680 vertebrate species to extinction since 1500
The threat of
extinction is also accelerating: in the best-studied taxonomic groups, most of
the total extinction risk to species is estimated to arisen in the past 40
years (established but incomplete) {2.2.5.2.4}.
The
proportion of species currently threatened with extinction according to the
IUCN Red List criteria averages around 25 per cent across the many terrestrial,
freshwater and marine vertebrate, invertebrate and plant groups that have been
studied in sufficient detail to support a robust overall estimate (established
but incomplete) {2.2.5.2.4, 3.2}
More than 40
per cent of amphibian species, almost a third of reef-forming corals, sharks
and shark relatives and over a third of marine mammals are currently threatened
{2.2.5.2.4, 3}.
The
proportion of insect species threatened with extinction is a key
uncertainty,but available evidence supports a tentative estimate of 10 per cent
(established but incomplete) {2.2.5.2.4}.
Those proportions suggest that, of an estimated 8 million animal and plant species (75% of which are insects), around 1 million are threatened with extinction (established but incomplete) {2.2.5.2.4}.
The Living
Planet Index, which synthesises trends in vertebrate populations, has declined
rapidly since 1970, falling by 40% for terrestrial species, 84% for freshwater
species and 35% for marine species (established but incomplete) {2.2.5.2.4}.
On land, wild
species that are endemic (narrowly distributed) have typically seen
larger-than-average changes to their habitats and shown faster-than-average
declines (established but incomplete) {2.2.5.2.3, 2.2.5.2.4}.
“A substantial proportion of assessed species are threatened with extinction and overall trends are deteriorating, with extinction rates increasing sharply in the past century. (A) Percentage of species threatened with extinction in taxonomic groups that have been assessed comprehensively, or through a ‘sampled’ approach, or for which selected subsets have been assessed, by the International Union for Conservation of Nature (IUCN) Red List of Threatened Species. Groups are ordered according to the best estimate for the percentage of extant species considered threatened (shown by the vertical blue lines), assuming that data deficient species are as threatened as non-data deficient species. (B) Extinctions since 1500 for vertebrate groups. Rates for reptiles and fishes have not been assessed for all species. (C) Red List Index of species survival for taxonomic groups that have been assessed for the IUCN Red List at least twice. A value of 1 is equivalent to all species being categorized as Least Concern; a value of zero is equivalent to all species being classified as Extinct. Data for all panels derive from http://www.iucnredlist.org (see Chapter 3 Figure 3.4 and Chapter 2 Figure 2.7).“
The number of
local varieties and breeds of domesticated plants and animals and their wild
relatives has been reduced sharply as a result of land use change, knowledge
loss, market preferences and large-scale trade (well established) {2.2.5.2.6,
2.2.5.3.1}.
Human-driven
changes in species diversity within local ecological communities vary widely,
depending on the net balance between species loss and the influx ofalien
species, disturbance-tolerant species, other human-adapted species or climate
migrant species (well established) {2.2.5.2.3}.
Many
organisms show ongoing biological evolution so rapid that it is detectable
within only a few years on even more quickly – in response to anthropogenic
drivers (well established) {2.2.5.2.5, 2.2.5.2.6}. Management decisions
that take those evolutionary changes into account will be noticeably more
effective (established but incomplete)
Drivers of observed changes to nature and ecosystem services
Direct and
indirect drivers of change have accelerated during the past 50 years
The rate of global change in nature during the past 50 years is unprecedented in human history. The direct drivers of change in nature with the largest global impact have been (starting with those with most impact): changes in land and sea use; direct exploitation of organisms; climate change; pollution; and invasion of alien species. Those five direct drivers result from an array of underlying causes – the indirect drivers of change – which are in turn underpinned by societal values and behaviours that include production and consumption patterns, human population dynamics and trends, trade, technological innovations and local through global governance. The rate of change in the direct and indirect drivers differs among regions and countries.
(IPBES) 2019 Global Assessment Report on Biodiversity and Ecosystem Services www.ipbes.net
I
have selected highlights from the policymaker summary and have largely followed
the sequence in that summary. I have
reorganized some sections and (for the most part), follow the order and
arrangement of the bold-faced sections in “Background” of the Summary, which
begins on page nine of the IPBES policy summary. The authors of the IPBES reports qualified
their conclusions/findings with expressions such as “well established,” “established but incomplete,”and
“inconclusive,” depending on the strength of studies and other criteria
underlying each area of concern. (See Global Trends table below). I include these comments, as well as the
sections in the various reports which further elaborate these findings. These sections are enclosed by { }. There is a vast amount of material in the
various reports, which are hyperlinked below.
Status of Nature and Ecosystem Services—Highlights from the Summary for Policymakers
(“Summary for policymakers of the global assessment report on
biodiversity and ecosystem services of the Intergovernmental Science-Policy
Platform on Biodiversity and Ecosystem Services” published in draft form 29 May
2019.) Summary
for Policymakers-Advance Draft
Nature and its vital contributions to
people, which together embody biodiversity and ecosystem functions and
services, are deteriorating worldwide
Nature’s goods and services: Global trends
Global trends in the capacity of
nature to sustain contributions to good quality of life from 1970 to the
present, which show a decline for 14 of the 18 categories of nature’s
contributions to people analyzed. Data supporting
global trends and regional variations come from a systematic review of over
2,000 studies {2.3.5.1}. Indicators were selected on the basis of
availability of global data, prior use in assessments and alignment with 18
categories. For many categories of nature’s contributions, two indicators are
included that show different aspects of nature’s capacity to contribute to
human well-being within that category. Indicators are defined so that an
increase in the indicator is associated with an improvement in nature’s
contributions.
Humanity is a dominant global influence on life on earth, and has caused natural terrestrial, freshwater and marine ecosystems to decline (well established)
Source: (“Summary for policymakers of the global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services” published in draft form 29 May 2019.) Summary for Policymakers-Advance Draft{} refer to chapters in the summary
Climate change is already having an impact on nature, from genes to ecosystems. It poses a growing risk owing to the accelerated pace of change and interactions with other direct drivers (well established) {2.1.12, 2.1.18,2.2.6.2}.
Unsustainable use of the Earth’s resources is underpinned by a set of demographic and economic indirect drivers that have increased, and that furthermore interact in complex ways, including through trade (well established) {2.1.6}.
Due to expansions
of infrastructure, extensive areas of the planet are being opened up to new
threats (well established) {2.1.11}
Long-distance
transportation of goods and people, including for tourism, have grown
dramatically in the past 20 years, with negative consequences for nature
overall (established but incomplete).
Distant areas of the world are increasingly connected, as consumption, production, and governance decisions increasingly influence materials, waste, energy, and information flows in other countries, generating aggregate economic gains while shifting economic and environmental costs, which can link to conflicts (established but incomplete)
Governance has at many levels moved slowly to further and better incorporate into policies and incentives the values of nature’s contributions to people. However, around the globe, subsidies with harmful effects on nature have persisted (well established) {2.1, 3, 5, 6.4}.
Governance has at many levels moved slowly to further and better incorporate into policies and incentives the values of nature’s contributions to people. However, around the globe, subsidies with harmful effects on nature have persisted (well established) {2.1, 3, 5, 6.4}.
USGS ecologists produced this map of mangrove deforestation in Burma’s (Myanmar’s) Irrawaddy Delta using an older version of the Global Land Survey dataset. Recent improvements are allowing them to map mangrove deforestation worldwide. (Map adapted by Robert Simmon from Giri et al., 2008.) NASA Earth Observatory Legend
Significance: Mangroves represent a unique ecosystem in
coastal area supporting a rich biodiversity and providing a range of nature’s
contribution to people including provisioning, regulating and supporting,
crucial for the sustenance of local communities. There ecosystem service benefits have been
valued at an average of 4200 US$/hectare/year.*
They provide coastal protection against storms and flooding, are
critical nursery habitats for fish, birds and marine mammals, act as effective
nutrient filters.* South-East Asian mangroves are among the most species
diverse in the world, having 268 plant species including 52 taxa growing
exclusively in mangrove habitat. Mangrove forests and forests soils can also
store significant amounts of organic carbon.*
Status: Recent changes in land use primarily for aquaculture has led to transformation of mangroves (up to 75 per cent in the last 3 decades. Mangroves exist in coastal areas where development demand is high and are being highly threatened by land-use change (see 4.1.2; 4.4.1). An estimated 1,140 km2 of mangroves have been lost between 2000 and 2012 in South-East Asia, with an average rate of 0.7-3.0 per cent per year.
Threats
include rapid urbanization (Philippines, Thailand, Vietnam), aquaculture (e.g.,
shrimp farming), paddy farming (Myanmar), expansion of oil palm (Malaysia and
Indonesia, including new development in Papua) (See
Figure above and chart below) In Asia, more than 50 per cent of
mangroves have been lost to support aquaculture, with 40 per cent of mangroves
in the Philippines lost to agriculture.
Indirect anthropogenic changes include those related to climate change—drought (e.g., Gulf of Carpentaria, Australia Nov-Dec 2016); rising sea levels pose a threat to mangroves in Bangladesh, New Zealand, Vietnam and China. Loss of mangrove forests and soils also removes carbon storage; Indonesia, Malaysia and Myanmar contributed 77% of global mangrove organic carbon storage loss between 2000-2015.*
*Source: Jonathan Sanderman et al 2018 A Global map of mangrove forest soil carbon at 30m resolution. Environ. Res. Lett. 13 055002
http:// https://www.ipbes.net/assessment-reports Top 20 nation rankings for (a) total mangrove area lost between the years 2000 and 2012, (b0 area loss as a percent of year 2000 mangrove area, (c) total soil organic carbon stocks, (d) carbon loss as a percent loss of year 2000 soil carbon stock. Range in values for (c) and (d) come from 25%-100% loss of carbon in upper meter in pixels identified as being deforested between the years 2000 and 2015.
Coral
reefs are the most diverse coastal ecosystems on earth and of disproportionate
ecological, economic and food security importance to the Asia-Pacific region
which has an inordinate proportion of the world’s healthy coral reefs. Coral diversity is highest in the Asia-Pacific
region.
The death of
reef-forming corals undermines resilience of coastal communities, and can lead
to the collapse of important coastal ecosystems.
One
third of reef- building corals in the region are threatened.
Loss
of habitat quality, heavy damage to entire reefs are major
threats in the region. In the case of El Niño event in 1998, 16 per cent of
the world’s coral reefs and 50 per cent of those in the Indian Ocean were
destroyed
Increase
in sea temperature and ocean acidification have been
projected as major drivers of change along coastal environments which may lead
to decline in coral reefs.
Increasing
outbreaks of crown of thorns starfish, a native predator that has boom
bust cycles linked to environmental pollution from farm lined estuaries
affected The Great Barrier Reef.
Coral
bleaching events are also increasingly devastating to the northern two thirds of
the reef over the last few years where coral-algae associations are disrupted
by high sea temperature. Habitats and
communities in the Great Barrier Reef ranged from poor to worsening at the end
of 2015, although some species like green turtle populations improved.
Among
the most serious emerging threats to coral reefs are coral diseases, which have
devastated coral populations throughout the Caribbean since the 1980s and
accompanied the mass coral bleaching there in 2005 and 2006. Over 90 per cent
of the main reef forming corals in the Caribbean have now died due to coral
disease with the severity of disease outbreaks commonly correlated with corals
stressed by bleaching. Coral diseases
are also being observed more frequently on Indo-Pacific reefs in heretofore
unrecorded places such the Great Barrier Reef, areas of Marovo Lagoon in the
Solomon Islands and the Northwestern Hawaiian Islands. The outbreaks seem to be
related to bacterial infections and other introduced disease organisms,
increasing pollution, human disturbance and increasing sea temperature, all of
which have put reef-forming corals at serious risk.
Marine ecosystems, from coastal to deep sea, now show the influence of human actions, with coastal marine ecosystems showing both large historical losses of extent and condition as well as rapid ongoing declines (established but incomplete) {2.2.5.2.1, 2.2.7.15}
Direct exploitation of fish and seafood has the largest relative impact in the oceans (well established) {2.2.6.2}.
The direct driver with the second highest impact on the oceans is the many changes in the uses of the sea and coast land (well established) {2.2.6.2} (See Summary of Observed Changes)
Distribution Of Changes In The Global Ocean
Source: Halpern
(B. S., Walbridge, S., Selkoe, K. A., Kappel, C. V., Micheli, F.,
D’Agrosa, C., … Watson, R. (2008). A Global Map of Human Impact on
Marine Ecosystems. Science, 319(5865), 948–952.doi:10.1126/science.1149345
1. Every square kilometer
of the ocean is affected by some anthropogenic driver of ecological change
2. Over 41% of the world’s oceans have medium to very high cumulative impacts:
North and Norwegian seas, South and East China seas, Eastern Caribbean, North American eastern seaboard, Mediterranean, Persian Gulf, Bering Sea, and the waters around Sri Lanka.
3. Lowest impact areas
include high-latitude Arctic and Antarctic poles, but this may change due to
future polar ice loss
4. Ecosystems with highest
impacts include hard and soft continental shelves and rocky reefs, andcoral reefs.
5. Habitat destruction and
alteration; e.g., coastal engineering; tourist development; salt marshes, mangroves, seagrass beds, coral
reefs
6. Input and transfer of
waterborne pathogens (runoff, aquaculture)
7. Air pollution
a. Toxic chemicals; e.g., POP’s over the Arctic zone by airborne volatilization;
b. Mercury
Source: Lavoie, R.A., Bouffard, A., Maranger, R.,
Amyot, M., 2018. Mercury transport and human exposure from global marine
fisheries. Sci. Rep. 8, 6705.
Significance: Human activities have increased the global circulation of mercury,a potent neurotoxin. Mercury can be converted into methylmercury, which biomagnifies along aquatic food chains and leads to high exposure in fish-eating populations.
Trends: Mercury export from the ocean increased over time as a function of fishing pressure, especially on upper-trophic-level organisms. In 2014, over 13 metric tonnes of mercury were exported from the ocean. Asian countries were important contributors of mercury export in the last decades and the western Pacific Ocean was identified as the main source.
Estimates of per capita mercury exposure through fish
consumption showed that populations in 38% of the 175 countries assessed,
mainly insular and developing nations, were exposed to doses of methylmercury
above governmental thresholds.
Given the high mercury intake through seafood consumption observed
in several understudied yet vulnerable coastal communities, we recommend a
comprehensive assessment of the health exposure risk of those populations.
Temporal trends (1950‒2014) of marine fisheries catches (dashed lines) and mercury exported (full lines). (a) Entire ocean (blue) and coastal (red) and high seas (orange) withbreakpoint (circle) ± standard error (horizontal line). (b) Entire ocean (blue) and trophic levels (TL) rounded to the nearest integer: 4 (red), 3 (orange), and 2 (green).
Nutrients (N,P): Eutrophication, Dead Zones
Plastics (shipping, fishing, land-based sources)
Microplastics (nanoparticles; food chain)
Macroplastics (ingestion, entanglement, habitat loss (shorelines))
Ocean plastic
can persist in sea surface waters, eventually accumulating in remote areas of
the world’s oceans.
Our model,
calibrated with data from multi-vessel and aircraft surveys, predicted at least
79 (45–129) thousand tonnes of ocean plastic are floating inside an area of 1.6
million km2; a figure four to sixteen times higher than previously
reported.
Over
three-quarters of the GPGP mass was carried by debris larger than 5 cm and at
least 46% was comprised of fishing nets. Microplastics accounted for 8% of the
total mass but 94% of the estimated 1.8 (1.1–3.6) trillion pieces floating in
the area.
Plastic
collected during our study has specific characteristics such as small
surface-to-volume ratio, indicating that only certain types of debris have the
capacity to persist and accumulate at the surface of the GPGP.
Finally, our results suggest that ocean plastic pollution within the GPGP is increasing exponentially and at a faster rate than the surrounding waters.
Decadal evolution of microplastic concentration in the GPGP. Mean (circles) and standard error (whiskers) of microplastic mass concentrations measured by surface net tows conducted in different decades, within (light blue) and around (dark grey) the GPGP. Dashed lines are exponential fits to the averages expressed in g km−2: f(x) = exp(a*x) + b, with x expressed in number of years after 1900, a = 0.06121, b = 151.3, R2 = 0.92 for within GPGP and a = 0.04903, b = −7.138, R2 = 0.78 for around the GPGP.
On a global scale, between 1984 and 2015, the loss of permanent land in coastal areas amounts to almost 28,000 km2, roughly equivalent to the surface area of Haiti (Fig. a). This is almost twice as large as the surface of gained land (about 14,000 km2) over the same period. On the other hand, the overall surface of gained active zone (about 25,000 km2) is more than two times larger than the surface of lost active zone (about 11,500 km2). Overall, the gain of active zone roughly balances the loss of land, and the gain of land balances the loss of active zone. This translates into a net loss of approximately 14,000 km2 of surface for human settlements and terrestrial ecosystems (Fig. b).
Source: Mentaschi, et al., Global long-term observations of coastal erosion and accretion, Scientific Reports volume 8, Article number: 12876 (2018) On a global scale, between 1984 and 2015, the loss of permanent land in coastal areas amounts to almost 28,000 km2, roughly equivalent to the surface area of Haiti (Fig. a). This is almost twice as large as the surface of gained land (about 14,000 km2) over the same period. On the other hand, the overall surface of gained active zone (about 25,000 km2) is more than two times larger than the surface of lost active zone (about 11,500 km2). Overall, the gain of active zone roughly balances the loss of land, and the gain of land balances the loss of active zone. This translates into a net loss of approximately 14,000 km2 of surface for human settlements and terrestrial ecosystems (Fig. b). Size distribution of cross-shore transition length above 50 m, for erosion and accretion of land (a) and active zone (b). Lost (c) and gained (d) land around the world; lost (f) and gained (g) active zone; balance gained – lost land (e) and active zone (h). Maps show the length of cross-shore erosion and accretion aggregated on coastal segments of 100 km. In all the maps the 4 spots with the highest local transition along a 250 m transect are indicated.
Drivers of shoreline change around the world
List of local cases of erosion/accretion discussed in Mentaschi, et al https://www.nature.com/articles/s41598-018-30904-w The legend provides for each spot a brief summary of the drivers of shoreline change
Land Loss in Coastal Areas: Shoreline modification “masks” true rates of shoreline change along the Atlantic Seaboard
Source: Armstrong, S. B., & Lazarus, E. D.( 2019). Masked shoreline erosion at
large spatial scales as a collective effect of beach nourishment. Earth’s Future, 7, 74– 84. https://doi.org/10.1029/2018EF001070
(R)ecent rates of shoreline change along the U.S. Atlantic Coast are, on average, less erosional than historical rates. This shift has occurred despite evidence of intensified environmental forcing, including acceleration in rates of relative sea‐level rise and increased significant wave height in offshore wave climates. We suggest that the use, since the 1960s, of beach nourishment as the predominant form of mitigation against chronic coastal erosion in the United States…could explain the unexpected reversal in shoreline‐change trends.
Using U.S. Geological Survey shoreline records from 1830–2007 spanning more than 2,500 km of the U.S. Atlantic Coast, we calculate a mean rate of shoreline change, prior to 1960, of −55 cm/year (a negative rate denotes erosion). After 1960, the mean rate reverses to approximately +5 cm/year, indicating widespread apparent accretion despite steady (and, in some places, accelerated) sea‐level rise over the same period.
Cumulative sediment input from decades of
beach‐nourishment projects may have sufficiently altered shoreline position to
mask “true” rates of shoreline change. Our
analysis suggests that long‐term rates of shoreline change typically used to
assess coastal hazard may be systematically underestimated. We also suggest
that the overall effect of beach nourishment along of the U.S. Atlantic Coast
is extensive enough to constitute a quantitative signature of coastal
geoengineering and may serve as a bellwether for nourishment‐dominated
shorelines elsewhere in the world.
The Anthropocene Dashboard 