4. Conclusions

component and the response time scale of the climate system, which is not considered in the GWP. Climatic impact assessment has been facing difficulties when comparing the effect of short- and long-lived GHGs. The GWP and GTP of longlived gases are the same [10]. However, for short-lived GHGs, the GWP does not

Therefore, the GTP has been proposed for the comparison of the impact of GHG

Overall the results estimated here are compiled in Table 7 in which the mini-

The CH4 emission estimation depends mainly on two factors, i.e., livestock population and CH4-specific emission factors of different types of livestock categories. Both the factor could be a source of uncertainty. For the livestock population database, we rely on livestock census taken from the reports published by the Government of India [29], and emission factors are collected from the IPCC report [20]. During livestock census, the database collection based on only 5% of the total livestock population is used for sampling purposes during the census, which is then aggregated into 100% data. This creates uncertainty in the methodology. Also, in IPCC guidelines 2006, three types of estimation methodology are proposed, i.e., basic method IPCC Tier 1, intermediate method IPCC Tier 2, and complex method IPCC Tier 3. As the method becomes advance, uncertainty related to methodology decreases. As found by Patra [30], Tier 1 method overestimates the CH4 emission by 15% compared to Tier 2 estimate. But, IPCC Tier 1 is readily available which covers for national or international level in combination with default emission

> GTP20 (Tg CO2e)

Minimum 0.12 4.06 0.01 0.00 0.00 0.00 Maximum 2.74 93.35 183.79 10.97 0.13 0.006 Average 0.43 14.93 29.22 1.74 0.02 0.001

Minimum 0.00 0.00 0.00 0.00 0.00 0.000 Maximum 0.11 3.82 7.53 0.45 0.002 0.003 Average 0.02 0.81 1.59 0.10 0.0005 0.0006

Results of CH4 emission and other climate metrics at national, state, and district levels.

15.3 523 1030 61.51 0.70 0.036

GTP100 (Tg CO2e)

ΔT<sup>20</sup> (mK) ΔT<sup>100</sup> (mK)

emissions on temperature changes at a specific time in future rather than the radiative forcing over a period of time [23]. Hence, we can say that the GTP compares temperatures at the end of a given time period due to GHG emissions. In comparison to GWP, GTP extends the information from radiative forcing to rise in the surface temperature relative to that of CO2 [11]. The GTP further extends the cause-effect chain by adding the temperature impact assessment in comparison with GWP and hence more relevant by comparing temperature changes [28]. The GTP is a function of time and used for analyzing the economic benefits from emission reduction. Therefore, it is useful to develop cost-effective policy for miti-

account the radiative forcing for a short period.

Climate Change and Agriculture

gation policies targeting temperature reduction.

mum, the maximum, and average are given.

CH4 (Tg year<sup>1</sup> )

Country level

State level

District level

Table 7.

164

GWP (Tg CO2e)

3.3 Uncertainty analysis

The findings of the study are CH4 emission, high GTP and surface temperature response at district level, state level, and national level in India. The total CH4 emission in India is 15.3 Tg in 2012, with the highest almost 92% of the emission occurring via enteric fermentation. The GTP due to CH4 emission at 20 and 100 year time horizon in India is 1030 Tg GTP20 CO2e and 62 Tg GTP100 CO2e, respectively. The livestock emission in India has the potential to cause the surface temperature rise up to 0.69 mK and 0.036 mK over 20 and 100 year time period, respectively. At a state level, the emission can cause the surface temperature response (ΔT) to vary from 8.49 � <sup>10</sup>�<sup>5</sup> to 1.25 � <sup>10</sup>�<sup>1</sup> mK in 20 year time horizon and from 4.23 � <sup>10</sup>�<sup>5</sup> to 6.25 � <sup>10</sup>�<sup>2</sup> mK in 100 year time horizon. On the other hand, at district level, the <sup>Δ</sup><sup>T</sup> varies from 1.53 � <sup>10</sup>�<sup>7</sup> to 0.005 mK in 20 years and from 7.66 � <sup>10</sup>�<sup>9</sup> to 0.0002 mK in 100 years' time frame. The GTP values of CH4 for 20 and 100 years are 67 and 4, respectively. The AGTP values for the same time horizons are 4.6 � <sup>10</sup>�<sup>14</sup> and 2.3 � <sup>10</sup>�<sup>15</sup> K kg�<sup>1</sup> . GTP is a metric, which is used in comparing multiple gases with reference to CO2, whereas AGTP is the absolute GTP giving temperature change per unit of GHG emission. Temperature indices like GTP and AGTP both give the surface temperature change and response using pulse emission. GTP of any greenhouse gas is equal to the ratio of AGTP of the given gas and AGTP of CO2. The AGTP measures the temperature change over the period of time after the GHG emission. It depends upon some factors such as climate sensitivity and ocean uptake of heat by the ocean. All of these factors response vary with the time horizon and may substantially modify climate metrics GTP and AGTP.

So, it follows a decreasing trend with an increase over the period of time from 20 to 100 years. GTP and AGTP follow the same pattern and also decrease with the year. These temperature indices GTP and AGTP both can be used to study the impact on surface temperature due to GHG emission with time. This finding helps to study the climate change impact on surface temperature from CH4 emission, which can cause climate damage over a short period of time, even emitted in small quantity.
