Ambitious mitigation pathways: Geophysical constraints

Transcription

1 Ambitious mitigation pathways: Geophysical constraints Roland Séférian CNRM (Météo-France/CNRS) Centre National de Recherches Météorologiques, Toulouse, France Conférence Coriolis - Polytechnique 11 Decembre 2017

2 Global Context GHG emissions and global mean temperature Anth. CO2 emissions [Gt CO2 y 1 ] (a) GCP2017 EDGARv4.2 Carbon Energy Decoupling? Global financial crisis Asian financial crisis Collapse of FSU US saving and loan crisis Oil crisis Anth. CH4 emissions [Tg CH4 y 1 ] Anth. N2O emissions [Tg N2O y 1 ] (b) EDGARv4.2 US EPA_2012 Oil crisis US saving and loan crisis (c) EDGARv4.2 US EPA_2012 US saving and loan crisis Oil crisis Global financial crisis Asian financial crisis Collapse of FSU Collapse of FSU Asian financial crisis Global financial crisis - Decadal stabilisation of CO 2 emissions (Le Quéré et al., 2017) - Other GHGs such as CH4 and N2O are rising still - Climate hiatus stops, global mean temperature continues to rise ~+0.88 C with respect to (preindustrial reference)

3 Framing the global response stringent mitigations SR1.5 mitigation pathways Net CO 2 Emissions [GtCO 2 y 1 ] (a) Temperature Anomaly [ C rel. to ] (b) Below 1.5 C 90th Below 1.5 C 66th Below 1.5 C 50th Return 1.5 C 66th Return 1.5 C 50th Return 1.5 C OS Below 2 C 66th Below 2 C 50th Above 2 C Time [years] Time [years].5 C by % of the stringent mitigation 50% 50% pathways 66% 66% halt warming below 1.5 C (c) - 20% the stringent mitigation pathways exceeds 1.5 C by mid-century and returns below by 2100 = overshooting scenarios e [ C decade 1 ] (d)

4 How are those pathways created? Suite of models and hypotheses - Integrated assessment models (assessed by IPCC working group III) - Earth system geophysical characteristics/im pacts are diagnosed but do not feedbacks - As a consequence: unlimited resources (space, water, nutrients and so on ) Diagnostics

5 Are CO 2 removal options unlimited? Reality check for stringent mitigation pathways Current human action Most used CO 2 removal option Efficiency/limits Smith et al., 2016

6 Assessing geophysical constraints an joint IAM-ESM study Net Carbon Emissions [PgC y 1] % 5% 10% 20% 30% E_2100= 0.5 PgC y 1 E_2100= 1.1 PgC y 1 E_2100= 1.6 PgC y 1 E_2100= 2.2 PgC y 1 E_2100= 2.6 PgC y 1 Stylized emissions pathways satisfy: (1) 2100 rcp2.5 carbon budget (1000 GtC, Peters et al., 2015) (2) 2030 INDC carbon emission level ( GtC) (3) Explore various rate of net negative CO 2 emissions by 2100 [from -2 to -10 GtC y-1]. (4) Other climate forcers and GHG are similar to those used in rcp26 shifted backward to 2016 Time [year] Séférian, Rocher and Guivarch, in review

7 Assessing geophysical constraints T from preindustrial [ C] Atmospheric CO2 [ppm] Primary Energy [EJ y 1] Carbon Emissions [GtC y 1] (a) Total Demand Supply (b) 0% 5% 10% 20% 30% Biomass Fossil (c) (d) IMACLIM results CNRM-ESM1 results - Net negative emissions by (i.e., carbon neutrality) - BECCS deployement starts in ~ Biomass Energy > Fossil fuel Energy by Peak in CO 2 concentration ~10-20% of the current level - T from preindustrial level exceeds 2 C but returns below 2 C or even 1.5 C Séférian, Rocher and Guivarch, in review

8 Assessing geophysical constraints Water Availability = RainFed water BECCS WaterNeeds CNRM-ESM1 results IMACLIM results Stringent 2030s Stringent (-) 2030s 2050s 2050s 2100s 2100s

9 Assessing geophysical constraints Land HeatWave [counts] (a) 0% 5% 10% 20% 30% - Increase in heatwave by about 120% in the less stringent mitigation pathways = would reduce carbon uptake efficiency - Follows the temperature overshoots Land Drought [counts] (b) - Double the occurence of drougt over land by midcentury - Potential tipping point

10 Questioning the fit-for-purpose of ESM/IAM: human-climate feedbacks? Macro-economics system (IAM) Earth system (ESM) Mitigation measures BECCS deployment Water needs/removals Climate Carbon Cycle Hydrological cycle Energy system (-) CO 2 reduction Water stocks (-) Carbon prices irrigation

11 Conclusions et perspectives - Ambitious mitigation pathways require a large amount of negative emissions - Negative emission technologies such as BECCS requires water to growth and takes up CO 2 - However, climate change could impact water stock and hence water availability for BECCS - To deploy BECCS at a nominal rate, on might balance water stress with irrigation which would cause an additional cost - This additional cost for BECCS technologies could push back the competitiveness of those low-carbon technologies, delaying mitigation measures - However, none of the model IAM and ESM are able to handle this kind of human-climate interactions - Because of this missing feedbacks, current models might provide a too optimistic view of mitigation pathways