Background legislation/decisions
 Paris Agreement prescribing a review of related progress every five years (Global Stocktake) to help the Parties update their
Nationally Determined Contributions (NDCs)
 Climate Change Adaptation Act (Act No. 50, 13 June 2018)
 Climate Change Adaptation Plan (Cabinet Decree, 27 November 2018)

 Assessment Report on Climate Change Impact in Japan (December 2020)

 MEXT & JMA have operated an advisory board for their climate change services since FY2018.
 Based on input from the MEXT/JMA Advisory Board on climate change services (established in FY 2018), the Climate Change inJapan assessment report was published in December 2020. A projection dataset is also to be produced in 2022 for updates on
physical science expertise and further contribution to climate-related action in Japan.

Details of Climate Change in Japan (2020) The report provides basic information contributing to climate change mitigation and adaptation / impact assessment for Japanesenational/local government bodies, commercial enterprises and the public.
 It covers the status of atmospheric greenhouse gases (GHGs) and observed/projected changes in climate variables (e.g., surface/sea
surface temperature, precipitation and sea levels) in and around the country.
 Climate conditions are generally projected under the RCP2.6 and 8.5 scenarios (referred to as the 2°C and 4°C Warming Scenarios in
the report), corresponding to potential climatic conditions with achievement of the Paris Agreement’s 2°C target and with nofuture additional mitigation measures, respectively.
 For certain long-term tendencies and projections, levels of confidence and uncertainty are indicated.
 In addition to the main publication, a separate detailed version is provided for climate change professionals/researchers and as
additional reference.
 The main publication provides an overview of the latest physical scientific expertise on climate change in and around Japan, serving as
an essential resource for related services and research.
 The chapter structure corresponds to individual climate components, allowing reference at any point based on the area of interest (e.g.,a GHG section on the causes of climate change, and a snow-related section for reference to news on mild winter conditions).
 This guide provides a breakdown of the report and outlines its background and characteristics.

1

Observed changes
 Atmospheric concentrations of greenhouse gases (GHGs) such as carbon dioxide (CO2), methane (CH4) and nitrous oxide(N2O) exhibit increasing trends in relation to human activity.
 There is an increasing trend in downward infrared radiation from the atmosphere corresponding to the intensity of thegreenhouse effect caused by GHGs.
Minamitorishima

Yonagunijima

CO2 mole fraction [ppm]RyoriAtmospheric concentrations of CO2 observed in Japan[year]

IPCC AR5/WG I report (2013) Atmospheric concentrations of GHGs have increased since 1750 due to human activity.
 Concentrations of CO2, CH4 and N2O have increased to levels unprecedented in the last 800,000 years or more. Mean
rates of increase in atmospheric concentrations over the past century are unprecedented in the last 22,000 years.

WMO Greenhouse Gas Bulletin No. 16 (2020)
 Globally averaged surface mole fractions for CO2 reached a new high in 2019 at 410.5 ± 0.2 ppm, corresponding to148% of pre-industrial levels.
 The mean annual absolute increase from 2010 to 2019 was 2.4 ppm/year (1.5 times that of the 1990s).

2 Climate projections are based on the 2/4°C Warming Scenarios (RCP2.6 and RCP8.5, respectively).
 Under the 2°C Warming Scenario, the global average surface temperature is likely to have risen by 0.9 – 2.3°C
by the end of the 21st century* from the pre-industrial level (0.3 – 1.7°C from the end of the 20th century*).
➡ This corresponds to potential climatic conditions with achievement of the Paris Agreement’s 2°C target.
 Under the 4°C Warming Scenario, the global average surface temperature is likely to have risen by 3.2 – 5.4°C
by the end of the 21st century* from the pre-industrial level (2.6 – 4.8°C from the end of the 20th century*).
➡ This corresponds to potential climatic conditions with no future additional mitigation measures.
* Averaged over 1986 – 2005 and 2081 – 2100, respectively(IPCC)

3

The term “projections” refers to averages over Japan at the end of the 21st century relative to the end of the 20th century orpresent, unless otherwise stated.
Projected values here are expressed as "approx. XX" based on averages, while the report itself shows values with specific uncertainty
ranges.

4

Observed changes
 The annual surface temperature over Japan (based on data from 15 observation stations considered to be relatively
uninfluenced by urbanization) increased at a rate of 1.24°C per century between 1898 and 2019.
 Between 1910 and 2019, the annual numbers of days with maximum temperatures of ≥ 30 and ≥ 35°C and minimum
temperatures of ≥ 25°C (referred to here as Tmax ≥ 30°C, Tmax ≥ 35°C and Tmin ≥ 25°C days, respectively) have increased,
while those of days with minimum temperatures of < 0°C (referred to here as Tmin < 0°C days) have decreased. In particular,
the number of Tmax ≥ 35°C days has increased significantly since the mid-1990s.
2°C Warming Scenario

4°C Warming Scenario

Potential conditions with achievement of theParis Agreement’s 2°C target

Potential conditions with no future
additional mitigation measures

Annual surface
temperature over Japan

Approx. 1.4°C increase

Approx. 4.5°C increase

Annual global averagesurface temperature

Approx. 1.0°C increase

Approx. 3.7°C increase

Tmax ≥ 35°C days per year

Approx. 2.8-day increase

Approx. 19.1-day increase

Tmin ≥ 25°C days per year

Approx. 9.0-day increase

Approx. 40.6-day increase

Tmin < 0°C days per year

Approx. 16.7-day decrease

Approx. 46.8-day decrease Under both scenarios, the annual surface temperature over Japan for the end of the
21st century is expected to increase, with more Tmax ≥ 35°C / Tmin ≥ 25°C days andfewer Tmin < 0°C days in many regions.
 The temperature increase over Japan is greater under the 4°C Warming Scenario thanunder the 2°C Warming Scenario.
 Under the same scenario, higher latitudes correspond to greater increases intemperature. Values are also higher in winter than in summer.
Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

Projection underthe 2°C Warming
Scenario

Projection underthe 4°C Warming
Scenario[°C]

Changes in annual surface temperature
for the end of the 21st century (2076 –
2095 average) relative to the end of the20th century (1980 – 1999 average)

5

Observed changes
 While the frequency of daily and hourly extreme precipitation has increased in Japan, that of wet days has decreased (bothstatistically significant).
 No statistically significant long-term trend is observed in annual or seasonal precipitation over Japan.

2°C Warming Scenario

4°C Warming Scenario

Potential conditions with achievement of the Paris
Agreement’s 2°C target

Potential conditions with no future additional
mitigation measures

Annual number of days with precipitation ≥ 200 mm

Approx. x 1.5 increase

Approx. x 2.3 increase

Annual number of events with precipitation ≥ 50 mm/h

Approx. x 1.6 increase

Approx. x 2.3 increase

Approx. 12% (15 mm) increase

Approx. 27% (33 mm) increase

No statistically significant change

Approx. 8.2-day increase

Annual maximum daily precipitation
Annual number of days with precipitation < 1.0 mm

Precipitation ≥ 50 mm/h is torrential rainfall rendering umbrellas useless and creating spray that impairs visibility.

 The frequency and intensity of daily and hourly extreme precipitation over Japan are expected to increase, while those of
wet days are expected to decrease.
 No statistically significant change in annual precipitation over Japan is projected.
There is significant uncertainty in projections on regional and prefectural scales.
 The precipitation system associated with the Baiu (seasonal rain) front in June is expected to intensify and be south of its
normal location.
The projection for July is characterized by significant uncertainty.
Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

6

Observed changes
 Data collected at observation stations on the Sea of Japan side of the country indicate that: the annual maximum snow depth in winter has decreased; and the annual number of days with snowfall ≥ 20 cm has decreased.

2°C Warming Scenario

4°C Warming Scenario

Potential conditions with achievementof the Paris Agreement’s 2°C target

Potential conditions with no future
additional mitigation measures

Annual maximum
snow depth andsnowfallApprox. 30% decrease

Approx. 70% decrease

Snowfall period/

Heavy snowfall(decadal max. in thepresent climate)(except Hokkaido andcertain other areas)/(except some areas of
Hokkaido)

Shorter(delayed start, early end)

Potential increase in Honshu
mountainous areas andHokkaido inland areas

 Outside inland Hokkaido, snowfall and snow depth are expected todecrease as global warming progresses, with a higher likelihood ofrain.

 Reduced snowfall amounts do not necessarily correspond to reduced
risk of exceedingly rare incidences of extremely heavy snowfall. It
should be noted that the confidence level of this projection is low.

A

B

C

D

E

F

G

Maximum snow depth in winter for the end of the 21st
century (2076 – 2095 average) standardized by that for theend of the 20th century (1980 – 1999 average) for A) all
Japan; B) Sea of Japan side of northern Japan; C) Pacific sideof northern Japan; D) Sea of Japan side of eastern Japan; E)
Pacific side of eastern Japan; F) Sea of Japan side of westernJapan; and G) Pacific side of western Japan. Grey, blue andred bars represent 1) observations for the end of the 20th
century, and projections for the end of the 21st century
under the 2) 2°C and 3) 4°C Warming Scenarios, respectively.

Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

7

Observed changes
 No long-term trend is observed in the number of typhoons approaching or making landfall on Japan.
 No long-term trend is observed in the number of strong typhoons or in their percentage among all typhoons.

 In and around Japan, the latitude of maximum typhoon intensity exhibited a northward shift.

 Numerous researchers have projected
increased typhoon intensity in the Japan
area due to greater amounts of atmosphericwater vapor, which is the driving force
behind typhoons.
 The results of 4°C warming simulations andother studies indicate high potential forincreased occurrence frequency* of intense
category 4 – 5 tropical cyclones over waters
south of Japan.
* The number of typhoons expected within a
specific area/period

Occurrence frequency deviation from recent climate conditions for
category 4 – 5 tropical cyclones with 4°C warming (1979 – 2010 average)(Yoshida et al., 2017)

 Globally The intensity of precipitation and wind associated with tropical cyclones (including typhoons) is expected to increase due togreater concentrations of atmospheric water vapor.
 The number of tropical cyclones is expected to decrease, although further research is needed to establish related
confidence.
Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

8

Observed changes
 Averaged sea surface temperatures (SSTs) around Japan increased at a rate of 1.14°C per century between 1900 and 2019.
 This exceeds the global average of 0.55°C per century. Rates of increase appear relatively high in continental sea areas
due to the warming tendency of land and the influence of warm currents.
 The degree of temperature increase depends on seasonal factors and sea areas.

Projection under the
2°C Warming Scenario

2°C Warming
Scenario

Projection under the
4°C Warming Scenario
Average forseas near Japan

Average forseas near Japan

Around Hokkaido
and eastern Japan

Around Hokkaido
and eastern Japan

Kanto
regionKanto
regionSouthern Japan

Southern Japan
Around Kyushu
and Okinawa

Potential conditions withachievement of the Paris
Agreement’s 2°C target

Potential conditions with nofuture additional mitigation
measuresAverage SST aroundJapan

Approx. 1.14°C
increase

Approx. 3.58°C
increase

Average global SST

Approx. 0.73°C
increase

Approx. 2.58°C
increase

Average global ocean
temperature (depth 0– 2,000 m)

Approx. 0.35°C
increase

Approx. 0.82°C
increase

Sea of Japan

Sea of Japan

Around Kyushu
and Okinawa

Expected changes in SST for the 2081 – 2100 average relative to the1986 – 2005 average
Asterisks denote statistical significance at 95% or more. No tendencyof statistical significance is observed for hash-marked areas.

4°C Warming
Scenario Under both scenarios, the average SST around Japan for the endof the 21st century is expected to increase.
 SST increase displays non-uniform characteristics, with significant
changes in the central part of the Sea of Japan under the 2°C
Warming Scenario and in the Kushiro/Sanriku area under the 4°C
Warming Scenario.
 Northward displacement of subtropical circulation due tonorthward shifting of westerly winds may cause SST increasearound Japan to exceed the global average. This may lead to highregional SST variability.

Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

9

Observed changes
 The global mean sea level (GMSL) increased by 0.16 m between 1902 and 2010 due to melting ice sheets/glaciers and seawater
expansion caused by ocean temperature increase. The average rate of sea level rise was 3.6 mm per year between 2006 and 2015,
which is approximately 2.5 times that observed between 1901 and 1990.

 A clear trend of sea level rise has been observed since 1980 along the Japanese coast, although some long-period variability(assumed to be natural) is predominant over the whole period.
 No statistically significant long-term trend is observed in the frequency/intensity of storm surges along the Japanese coast.
 The heights of extreme waves along the Japanese coast show an increasing tendency, which is larger on the Pacific side.

 Under both scenarios, mean sea level rise along the Japanese
coast by the end of the 21st century is expected to match theglobal mean.
 No remarkable difference is observed among projected
regional rises except for coastal areas influenced directly by
the warm Kuroshio current, where levels are expected to riseslightly.

2°C Warming
Scenario

4°C Warming
Scenario

Potential conditions withachievement of the Paris
Agreement’s 2°C target

Potential conditions with nofuture additional mitigation
measures

Mean sea level
along the Japanese
coast

Approx. 0.39 m
increase

Approx. 0.71 m
increase

Global mean sea level

Approx. 0.39 m
increase

Approx. 0.71 m
increase

Projection under the
2°C Warming Scenario

Projection under the
4°C Warming Scenario

 The projected sea level rise suggests an enhanced risk offlooding.

 The scale of maximum storm surges in the bays of Tokyo,
Osaka and Ise are expected to increase (dependent on
typhoon projection).
 Wave heights in decadal-scale events are expected to increase
along the Japanese coast (with low confidence due to highuncertainty in the projection of typhoon path changes).

⚫ Sites / I – IV: Regions

Region I

II

III

along theIV MeanJapanese coast

Region I

II

III

along theIV MeanJapanese coast

Mean sea level rise along the Japanese coast for the end of the
21st century relative to the end of the 20th century

Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

10

Observed changes

Around the end of the 20th century(1986 – 2005 average)

Observed
Month

Sea ice extent [106 km2]

Sea ice extent [106 km2]

 The annual maximum Sea of Okhotsk ice extent decreased at a rate of 61,000 km2 (equivalent to 5.3% of the normal annual
maximum) per decade between 1971 and 2020.
 Observation data for the Japanese coast of the Sea of Okhotsk since 1956 indicate a remarkable reduction in drift ice
amounts since the second half of the 1980s.
 The annual minimum Arctic Sea ice extent decreased at a rate of 890,000 km2 (equivalent to 14% of the normal annual
minimum) per decade between 1979 and 2019.
 No statistically significant change is observed in the Antarctic Sea ice extent.

2°C Warming Scenario 4°C Warming Scenario

End of the 21st century(2081 – 2100 average)

Month

Potential conditions withachievement of the Paris
Agreement’s 2°C target

Potential conditions with nofuture additional mitigation
measures

Sea of Okhotsk ice
extent for MarchApprox. 28% decrease

Approx. 70% decrease

Arctic Sea ice extent
for February

Approx. 8% decrease

Approx. 34% decrease

Arctic Sea ice extent
for September

Approx. 43% decrease

Approx. 94% decrease

Seasonal changes in Sea of Okhotsk ice extent

 The Sea of Okhotsk ice extent in March for the end of the 21st century is expected to decrease under both scenarios, although
the reduction under the 2°C Warming Scenario would be within the range of variability in the present climate.
 The amount of sea ice drifting toward the Hokkaido coast is expected to decrease along with reduced sea ice formation along
the Siberian coast.
 Arctic Sea ice extent/thickness is highly likely to decrease during the 21st century, falling to practically zero by the mid-21st
century under the 4°C Warming Scenario.
Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

11

Observed changes
 Around 30% of anthropogenic CO2 emitted into the atmosphere is absorbed by oceans, which causes the hydrogen ion
exponent (pH) of global surface seawater to decrease at a rate of approx. 0.02 per decade. The global average surface
seawater pH is estimated to have decreased by 0.1 since the onset of industrialization.
 Observation data collected from 137°E since 1983 indicate ongoing acidification at a rate similar to the global average (pHvalues are generally reduced at lower latitudes, where the sea surface temperature is higher).
 A tendency of acidification is also seen along the Japanese coast, with pH values between 1978 and 2009 decreasing by
0.014 and 0.024 per decade in summer and winter (the annual lowest and highest, respectively). These rates are similar to
those seen in open seas.

2°C Warming Scenario

4°C Warming Scenario

Potential conditions with achievementof the Paris Agreement’s 2°C target

Potential conditions with no future
additional mitigation measures

Surface seawater pH
south of Japan

Approx. 0.04 decrease

Approx. 0.3 decrease

Surface seawater pH(global average)

Approx. 0.065 decrease by
the mid-21st century andstable thereafter

Approx. 0.31 decrease

Annual average Ωarag
around Okinawa

Ongoing decrease until themid-21st century
3 or more

Below 3 seasonally in the
2020s – 2030s
Below 3 throughout the year
after around 2050

Annual average Ωarag
south of Japan

Approx. 0.2 decrease

Approx. 1.4 decrease

Annual average Ωarag(global average)/

Below 3 by 2060
except in low latitudes

 Globally, pH values are expected to fall
rapidly in polar and high-latitude regions.
 Aragonite
saturation(Ωarag)indicates
acidification in the marine ecosystem. Ωarag in
high-latitude regions is expected to fall
below 3 (a guidance value for significant
effects on coral reefs) earlier than in thesubtropical zone, even though the rate ofdecrease is higher in the latter.
 Increasing
ocean
acidification
aroundOkinawa and southern Japan is expected at a
rate similar to that of the global average.

Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

12

Projected climate conditions for areas in and around Japanfor the end of the 21st century relative to the end of the 20th century or present:

Yellow and purple figures represent
the 2°C and 4°C Warming Scenarios(RCP2.6 and 8.5 scenarios), respectively.

Sea Surface Temperature
Increase: approx. 1.14 / 3.58°C

Annual Surface Temperature

Increase: approx. 1.4 / 4.5°C

The degree of increase is greater than the global
average due to geographical characteristics (i.e.,
greater continental warming than that from ocean
and warm currents).
with more Tmax ≥ 35°C days,
more Tmin ≥ 25°C days
and fewer Tmin < 0°C days

Snowfall and Snow Depth
Decrease
Rainfall rather than snow
Ongoing risk of heavy snow

Increased sea levels

along the Japanese coast by factors ofapprox. 0.39 / 0.71 m

Heavy Precipitation
Frequency Increase
Annual maximum daily precipitation increaseof approx. 12% (15 mm) / 27% (33 mm)

Reduced Sea of Okhotsk Ice Extent
in March by approx. 28 / 70%
The Arctic Sea is expected to bepractically ice-free by the mid-21st century
under the 4°C Warming Scenario.

Precipitation ≥ 50 mm/h event increaseby factors of approx. 1.6 / 2.3

Proportion ofStrong-Typhoon Increase

Ongoing Ocean Acidification

Increased Wind Speedand Precipitation

Similar to those of the Global Averagearound Okinawa and southern Japan

Associated with Typhoons

Projections are averages over Japan for the end of the 21st century relative to the end of the 20th century or present, unless otherwise stated.

13

IPCC Special Report on Global Warming of 1.5°C (2018)
 Global warming is likely to reach 1.5°C between 2030 and 2052 if it continues to increase at the current rate.
 In model pathways with no or limited overshoot of 1.5°C, global net anthropogenic CO2 emissions decline byapprox. 45% from 2010 levels by 2030 (40 – 60% interquartile range), reaching net zero around 2050 (2045 – 2055
interquartile range).
 For limiting global warming to below 2°C, CO2 emissions are expected to decline by approx. 25% by 2030 in mostpathways (10 – 30% interquartile range) and reach net zero around 2070 (2065 – 2080 interquartile range).

(IPCC)

14