{
 "page": "https://factchecked.science/next-excursion/",
 "title": "When is the next magnetic excursion due?",
 "checked": "2026-10-12",
 "about": "Every number on the page, with where it comes from. ‘decline.py’ and ‘pattern.py’ are the scripts published beside this file; ‘from’ gives the key in the JSON each one writes (decline.json, pattern.json). ‘value’ is the unrounded result and ‘shown’ the page’s wording. Numbers in square brackets refer to the page’s source list.",
 "conventions": {
  "ages": "Ages count back from AD 1950 (‘before present’), as in the sources. An age of t years is the year 1950 − t; zero or negative years are BC on the astronomical count (year 0 = 1 BC, −1059 = 1060 BC).",
  "today": "The page marks today as 2026. Counting ages back from 2026 instead of 1950, as the original infographic did, shifts every date by 76 years.",
  "decline": "The axial dipole is |g10| from IGRF-14 [2]. Percentages are of its 2025 value, 29,350 nT. Paces are nanotesla a year of weakening; projections start in 2025 and run to 5% of the 2025 value. Two thresholds are marked: half today’s strength, about where past excursions began ([29]; [18] §4.4, about half the present-day field, 40 ZAm2), and about 5%, the deepest point of Laschamp in the LSMOD.2 model [18], as Larsen and colleagues compute it ([6] §3).",
  "thresholds_percent_of_2025": {
   "half_strength_where_excursions_began": 50,
   "laschamp_low": 5,
   "long_term_average_one_study": 60
  }
 },
 "events": [
  {
   "name": "Tianchi",
   "age_years_before_1950": 7000,
   "sigma_years": 450,
   "sigma_is_our_estimate": false,
   "calendar_year": "5051 BC",
   "basis": "7.0 ± 0.9 ka at 95% confidence, so one sigma is taken as half of that, 0.45 ka. An earlier age of about 8.1 ka rested on indirect dates from radiocarbon, stratigraphy and ash layers ([23] p. 1); see the Tianchi 8,100 variant",
   "sources": [
    "[23] Pan et al. 2022"
   ],
   "distance_to_nearest_comb_tooth_years": 110
  },
  {
   "name": "Gothenburg",
   "age_years_before_1950": 14450,
   "sigma_years": 250,
   "sigma_is_our_estimate": true,
   "calendar_year": "12501 BC",
   "basis": "First reported in 1971 from a core in Gothenburg’s Botanical Garden [31]. Type section ‘12,400−12,350 years BP’ in radiocarbon years [24]; IntCal20 calibration of 12,350 ± 100 gives a median of 14,447 cal BP (95%: 14,095–14,925). Calibration done separately; not in the hosted scripts",
   "sources": [
    "[31] Mörner, Lanser and Hospers 1971",
    "[24] Mörner 1977",
    "[27] IntCal20"
   ],
   "distance_to_nearest_comb_tooth_years": 757
  },
  {
   "name": "Hilina Pali",
   "age_years_before_1950": 19500,
   "sigma_years": 1000,
   "sigma_is_our_estimate": true,
   "calendar_year": "17551 BC",
   "basis": "19.5 ± 1.0 ka from the best-dated record, varve-counted lake sediments in Arctic Russia: 19.0–20.3 ka [20]. The Hawaiian type lavas were dated 19.3 ± 1.6 ka in an earlier calibration of their radiocarbon ages ([23] p. 5). Other records give about 17–21.5 ka ([20] Table 1); see the Hilina Pali variants",
   "sources": [
    "[20] Scheidt et al. 2025",
    "[23] Pan et al. 2022"
   ],
   "distance_to_nearest_comb_tooth_years": 996
  },
  {
   "name": "Rockall",
   "age_years_before_1950": 26500,
   "sigma_years": 500,
   "sigma_is_our_estimate": true,
   "calendar_year": "24551 BC",
   "basis": "26.35–26.70 ka, from a single core",
   "sources": [
    "[19] Channell et al. 2016"
   ],
   "distance_to_nearest_comb_tooth_years": 799
  },
  {
   "name": "Mono Lake",
   "age_years_before_1950": 34500,
   "sigma_years": 1000,
   "sigma_is_our_estimate": true,
   "calendar_year": "32551 BC",
   "basis": "About 34.5 ka in several records",
   "sources": [
    "[16] Liu et al. 2020",
    "[17] Ali et al. 2026",
    "[28] Nowaczyk et al. 2025"
   ],
   "distance_to_nearest_comb_tooth_years": 398
  },
  {
   "name": "Laschamp",
   "age_years_before_1950": 41100,
   "sigma_years": 350,
   "sigma_is_our_estimate": false,
   "calendar_year": "39151 BC",
   "basis": "41.10 ± 0.35 ka. The published ± allows for the sampling resolution, and its uranium–thorium dates are two-sigma; we use it as one sigma (the difference is negligible here)",
   "sources": [
    "[15] Lascu et al. 2016"
   ],
   "distance_to_nearest_comb_tooth_years": 195
  }
 ],
 "older_events": [
  {
   "name": "Norwegian–Greenland Sea",
   "age_years_before_1950": 64500,
   "sigma_years": 1500,
   "distance_to_nearest_comb_tooth_years": 3186,
   "note": "About 64.5 ka [16]"
  },
  {
   "name": "Post-Blake",
   "age_years_before_1950": 99500,
   "sigma_years": 5500,
   "distance_to_nearest_comb_tooth_years": 2632,
   "note": "Our catalog’s age; not re-checked against primary sources"
  },
  {
   "name": "Blake",
   "age_years_before_1950": 115000,
   "sigma_years": 3000,
   "distance_to_nearest_comb_tooth_years": 738,
   "note": "Our catalog’s age; not re-checked against primary sources"
  },
  {
   "name": "Iceland Basin",
   "age_years_before_1950": 189000,
   "sigma_years": 2000,
   "distance_to_nearest_comb_tooth_years": 1571,
   "note": "About 188 ka in [14]"
  },
  {
   "name": "Pringle Falls",
   "age_years_before_1950": 211000,
   "sigma_years": 6500,
   "distance_to_nearest_comb_tooth_years": 20,
   "note": "211–238 ka in [14]"
  }
 ],
 "pattern": {
  "gaps_years": {
   "value": [
    7450,
    5050,
    7000,
    8000,
    6600
   ],
   "shown": "",
   "from": "pattern.py verified.gaps_ka"
  },
  "average_gap_years": {
   "value": 6820,
   "shown": "6,800-year average gap",
   "from": "pattern.py verified.average_gap_ka"
  },
  "comb_period_years": {
   "value": 6803,
   "shown": "6,800 years",
   "from": "pattern.py verified.comb_weighted_step0.001.P"
  },
  "comb_latest_tooth_AD": {
   "value": 1863,
   "shown": "about AD 1860",
   "from": "pattern.py verified.tooth_nearest_present_AD_BP1950"
  },
  "comb_tooth_before_that_years_before_1950": {
   "value": 6890,
   "shown": "about 7,000 years ago, beside Tianchi",
   "from": "pattern.py verified.last_tooth_ka + P"
  },
  "comb_next_future_tooth_AD": {
   "value": 8666,
   "shown": "around AD 8700",
   "from": "pattern.py verified.next_tooth_AD_BP1950"
  },
  "line_centre_AD": {
   "value": 1873,
   "shown": "about AD 1870",
   "from": "pattern.py verified.pi_line_own_center_AD_BP1950"
  },
  "prediction_interval_halfwidth_years": {
   "value": 2932,
   "shown": "±2,930 years (‘give or take 3,000 years’)",
   "from": "pattern.py verified.pi_halfwidth_years"
  },
  "prediction_interval_AD": {
   "value": [
    -1059,
    4806
   ],
   "shown": "roughly 1100 BC to AD 4800",
   "from": "pattern.py verified.pi_line_own_AD_range_BP1950"
  },
  "due_by_average_gap_AD": {
   "value": 1770,
   "shown": "AD 1770",
   "from": "pattern.py verified.due_by_avg_gap_AD_BP1950"
  },
  "years_overdue_in_2026": {
   "value": {
    "comb": 163,
    "average_gap": 256
   },
   "shown": "due about 160 to 260 years ago",
   "from": "2026 minus the two dates above"
  },
  "teeth_to_215000_years": {
   "value": 32,
   "shown": "32 teeth",
   "from": "pattern.py verified.teeth_0_215"
  },
  "teeth_with_event_within_1000_years": {
   "value": 8,
   "shown": "8 of 32",
   "from": "pattern.py verified.teeth_hit_within_1kyr"
  },
  "teeth_hit_years_before_1950": {
   "value": [
    6890,
    13690,
    20500,
    27300,
    34100,
    40910,
    115740,
    210980
   ],
   "shown": "six in the fitted stretch, plus Blake and Pringle Falls",
   "from": "pattern.py verified.teeth_hit_list"
  },
  "teeth_hit_with_other_ages_for_Blake_and_Pringle_Falls": {
   "value": {
    "Pringle Falls 238 ka": 7,
    "Blake 116 ka": 8,
    "Blake 112 ka": 7
   },
   "shown": "7 or 8",
   "from": "pattern.py verified.teeth_hit_PF238 / _Blake116 / _Blake112"
  },
  "older_events_mean_distance_to_tooth_years": {
   "value": 1629,
   "shown": "1,630 years",
   "from": "pattern.py verified.older_mean_offset_ka"
  },
  "random_dates_mean_distance_to_tooth_years": {
   "value": 1701,
   "shown": "1,700 years",
   "from": "pattern.py verified.chance_mean_offset_ka (P/4)"
  },
  "p_random_older_dates_this_close": {
   "value": 0.4379,
   "shown": "p = 0.44",
   "from": "pattern.py verified.p_older_this_close_by_chance"
  },
  "runback_test_power": {
   "value": {
    "mean_offset_if_on_teeth_ka": 1.545,
    "chance_mean_offset_ka": 1.701,
    "share_of_simulations_with_p_below_0.05": 0.097,
    "median_p_if_on_teeth": 0.372,
    "simulations": 2000
   },
   "shown": "even if each sat on a tooth, dating errors alone would leave them about 1,550 years away (random dates: 1,700); the test reaches p < 0.05 in about 10% of such simulations",
   "from": "pattern.py runback_power (older events placed on their nearest teeth, then shifted by their one-sigma errors; seed 20261012)"
  },
  "spacing_cv": {
   "value": 0.1467,
   "shown": "0.15 (‘about 15%’)",
   "from": "pattern.py verified.cv"
  },
  "spacing_cv_random_median": {
   "value": 0.751,
   "shown": "about 0.75",
   "from": "pattern.py verified.cv_random_median"
  },
  "chance_spacing_this_even": {
   "value": 0.00102,
   "shown": "about 0.1%, about once in a thousand tries",
   "from": "pattern.py verified.p_cv (100,000 catalogues)"
  },
  "chance_with_dating_errors_median_and_90th_percentile_case": {
   "value": [
    0.0026,
    0.0139
   ],
   "shown": "typically 0.26%",
   "from": "pattern.py verified.p_cv_at_jitter_q10_50_90[1:]"
  },
  "chance_with_minimum_gap_3_4_5_thousand_years": {
   "value": [
    0.0104,
    0.0279,
    0.082
   ],
   "shown": "3–8% for 4,000–5,000 years",
   "from": "pattern.py verified.p_cv_mingap_3/4/5"
  },
  "chance_spacing_this_even_by_hilina_pali_age": {
   "value": {
    "17,000 years": 0.02896,
    "17,500 years": 0.01701,
    "18,000 years": 0.00897,
    "18,500 years": 0.00456,
    "19,000 years": 0.00236,
    "19,300 years": 0.00123,
    "19,500 years": 0.00102,
    "20,000 years": 0.00056,
    "20,500 years": 0.00044
   },
   "shown": "0.04% at 20,500 years, 0.5% at 18,500 and about 3% at 17,000",
   "from": "pattern.py verified_HP*.p_cv and verified.p_cv"
  },
  "grid_6000_years_share_of_random_dates_as_close": {
   "value": 0.651,
   "shown": "65% of the time",
   "from": "pattern.py verified.grid6_p_random_as_close"
  },
  "all_11_events_cv_vs_random_median": {
   "value": [
    0.986,
    0.851
   ],
   "shown": "0.99 against 0.85",
   "from": "pattern.py verified.cv_all11, cv_all11_random_median"
  },
  "excursions_implied_since_last_reversal": {
   "value": 114.7,
   "shown": "over 100 excursions since the last reversal; reviews list 12 to 17 [14]",
   "from": "pattern.py verified.excursions_implied_since_last_reversal (780,000 years / comb period)"
  },
  "comb_tooth_range_across_single_age_variants_AD": {
   "value": [
    1078,
    3658
   ],
   "shown": "between about AD 1100 and 3700",
   "from": "pattern.py tooth_nearest_present_AD_BP1950 across the verified and verified_* variants"
  },
  "comb_tooth_for_single_ages_AD": {
   "value": {
    "Tianchi 8,100": 1078,
    "Gothenburg 12,800": 2722,
    "Hilina Pali 17,000": 3658
   },
   "shown": "near AD 1100, 2700 and 3700",
   "from": "pattern.py verified_Tianchi8.1 / verified_Goth12.8 / verified_HP17 .tooth_nearest_present_AD_BP1950"
  }
 },
 "pattern_age_variants": [
  {
   "variant": "Verified ages (used on the page)",
   "pattern_py_key": "verified",
   "comb_period_years": 6803,
   "comb_tooth_nearest_present_AD": 1863,
   "line_centre_AD": 1873,
   "prediction_interval_halfwidth_years": 2932,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "8 of 32",
   "spacing_cv": 0.1467,
   "chance_spacing_this_even": 0.00102,
   "excursions_implied_since_last_reversal": 114.7
  },
  {
   "variant": "Ages behind the original infographic",
   "pattern_py_key": "infographic",
   "comb_period_years": 6879,
   "comb_tooth_nearest_present_AD": 2426,
   "line_centre_AD": 2110,
   "prediction_interval_halfwidth_years": 2498,
   "due_by_average_gap_AD": 1170,
   "teeth_with_event_within_1000_years": "5 of 31",
   "spacing_cv": 0.1162,
   "chance_spacing_this_even": 0.00052,
   "excursions_implied_since_last_reversal": 113.4
  },
  {
   "variant": "Hilina Pali 17,000 (one lake record; also the Tianchi lava’s superseded argon age)",
   "pattern_py_key": "verified_HP17",
   "comb_period_years": 8850,
   "comb_tooth_nearest_present_AD": 3658,
   "line_centre_AD": 2540,
   "prediction_interval_halfwidth_years": 6636,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "3 of 24",
   "spacing_cv": 0.3423,
   "chance_spacing_this_even": 0.02896,
   "excursions_implied_since_last_reversal": 88.1
  },
  {
   "variant": "Hilina Pali 17,500",
   "pattern_py_key": "verified_HP17.5",
   "comb_period_years": 8835,
   "comb_tooth_nearest_present_AD": 3545,
   "line_centre_AD": 2407,
   "prediction_interval_halfwidth_years": 5832,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "3 of 24",
   "spacing_cv": 0.2991,
   "chance_spacing_this_even": 0.01701,
   "excursions_implied_since_last_reversal": 88.3
  },
  {
   "variant": "Hilina Pali 18,000",
   "pattern_py_key": "verified_HP18",
   "comb_period_years": 6801,
   "comb_tooth_nearest_present_AD": 1844,
   "line_centre_AD": 2273,
   "prediction_interval_halfwidth_years": 5044,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "7 of 32",
   "spacing_cv": 0.2569,
   "chance_spacing_this_even": 0.00897,
   "excursions_implied_since_last_reversal": 114.7
  },
  {
   "variant": "Hilina Pali 18,500",
   "pattern_py_key": "verified_HP18.5",
   "comb_period_years": 6811,
   "comb_tooth_nearest_present_AD": 1924,
   "line_centre_AD": 2140,
   "prediction_interval_halfwidth_years": 4284,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "7 of 32",
   "spacing_cv": 0.2165,
   "chance_spacing_this_even": 0.00456,
   "excursions_implied_since_last_reversal": 114.5
  },
  {
   "variant": "Hilina Pali 19,000",
   "pattern_py_key": "verified_HP19",
   "comb_period_years": 6811,
   "comb_tooth_nearest_present_AD": 1924,
   "line_centre_AD": 2007,
   "prediction_interval_halfwidth_years": 3570,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "7 of 32",
   "spacing_cv": 0.179,
   "chance_spacing_this_even": 0.00236,
   "excursions_implied_since_last_reversal": 114.5
  },
  {
   "variant": "Hilina Pali 19,300",
   "pattern_py_key": "verified_HP19.3",
   "comb_period_years": 6811,
   "comb_tooth_nearest_present_AD": 1932,
   "line_centre_AD": 1927,
   "prediction_interval_halfwidth_years": 3175,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "7 of 32",
   "spacing_cv": 0.1588,
   "chance_spacing_this_even": 0.00123,
   "excursions_implied_since_last_reversal": 114.5
  },
  {
   "variant": "Hilina Pali 20,000",
   "pattern_py_key": "verified_HP20",
   "comb_period_years": 6793,
   "comb_tooth_nearest_present_AD": 1772,
   "line_centre_AD": 1740,
   "prediction_interval_halfwidth_years": 2435,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "8 of 32",
   "spacing_cv": 0.1236,
   "chance_spacing_this_even": 0.00056,
   "excursions_implied_since_last_reversal": 114.8
  },
  {
   "variant": "Hilina Pali 20,500",
   "pattern_py_key": "verified_HP20.5",
   "comb_period_years": 6782,
   "comb_tooth_nearest_present_AD": 1666,
   "line_centre_AD": 1607,
   "prediction_interval_halfwidth_years": 2176,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "8 of 32",
   "spacing_cv": 0.1155,
   "chance_spacing_this_even": 0.00044,
   "excursions_implied_since_last_reversal": 115.0
  },
  {
   "variant": "Gothenburg 12,800 (another record)",
   "pattern_py_key": "verified_Goth12.8",
   "comb_period_years": 6953,
   "comb_tooth_nearest_present_AD": 2722,
   "line_centre_AD": 2643,
   "prediction_interval_halfwidth_years": 2466,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "6 of 31",
   "spacing_cv": 0.1043,
   "chance_spacing_this_even": 0.00026,
   "excursions_implied_since_last_reversal": 112.2
  },
  {
   "variant": "Gothenburg 13,900 (if a marine reservoir correction applied)",
   "pattern_py_key": "verified_Goth13.9",
   "comb_period_years": 6845,
   "comb_tooth_nearest_present_AD": 2115,
   "line_centre_AD": 2130,
   "prediction_interval_halfwidth_years": 2495,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "6 of 31",
   "spacing_cv": 0.113,
   "chance_spacing_this_even": 0.00036,
   "excursions_implied_since_last_reversal": 114.0
  },
  {
   "variant": "Tianchi 7,370 (charcoal under the lava)",
   "pattern_py_key": "verified_Tianchi7.4",
   "comb_period_years": 6747,
   "comb_tooth_nearest_present_AD": 1588,
   "line_centre_AD": 1627,
   "prediction_interval_halfwidth_years": 3031,
   "due_by_average_gap_AD": 1326,
   "teeth_with_event_within_1000_years": "7 of 32",
   "spacing_cv": 0.1429,
   "chance_spacing_this_even": 0.00103,
   "excursions_implied_since_last_reversal": 115.6
  },
  {
   "variant": "Tianchi 8,100 (an earlier, indirect age from radiocarbon, stratigraphy and its ash)",
   "pattern_py_key": "verified_Tianchi8.1",
   "comb_period_years": 6644,
   "comb_tooth_nearest_present_AD": 1078,
   "line_centre_AD": 1140,
   "prediction_interval_halfwidth_years": 3424,
   "due_by_average_gap_AD": 450,
   "teeth_with_event_within_1000_years": "5 of 33",
   "spacing_cv": 0.1451,
   "chance_spacing_this_even": 0.00098,
   "excursions_implied_since_last_reversal": 117.4
  },
  {
   "variant": "Mono Lake 34,000 ± 1,500",
   "pattern_py_key": "verified_Mono34",
   "comb_period_years": 6772,
   "comb_tooth_nearest_present_AD": 1829,
   "line_centre_AD": 1807,
   "prediction_interval_halfwidth_years": 2744,
   "due_by_average_gap_AD": 1770,
   "teeth_with_event_within_1000_years": "9 of 32",
   "spacing_cv": 0.1328,
   "chance_spacing_this_even": 0.00062,
   "excursions_implied_since_last_reversal": 115.2
  }
 ],
 "decline": {
  "g10_2025_nT": {
   "value": 29350.0,
   "shown": "",
   "from": "decline.py g10_abs_nT.2025"
  },
  "lost_since_1840_percent": {
   "value": 8.9,
   "shown": "9%",
   "from": "decline.py loss_since_1840_pct"
  },
  "loss_per_century_percent_linear_compound": {
   "value": [
    4.81,
    4.91
   ],
   "shown": "about 5% per century",
   "from": "decline.py loss_per_century_*"
  },
  "value_1840_percent_of_2025": {
   "value": 109.77,
   "shown": "",
   "from": "decline.py pct_of_2025_in_1840"
  },
  "value_1590_percent_of_2025": {
   "value": 111.47,
   "shown": "",
   "from": "decline.py pct_of_2025_in_1590"
  },
  "five_year_pace_since_1945_min_max_nT_per_year": {
   "value": [
    {
     "from": 2015,
     "to": 2020,
     "nT_per_yr": 7.61
    },
    {
     "from": 1970,
     "to": 1975,
     "nT_per_yr": 24.0
    }
   ],
   "shown": "between 7.6 and 24 nT a year",
   "from": "decline.py since_1945_min, since_1945_max"
  },
  "forecast_pace_2025_30_nT_per_year": {
   "value": 12.6,
   "shown": "12.6 nT a year",
   "from": "decline.py sv_g10_2025_2030_nT_per_yr"
  },
  "pace_now_vs_1980_85": {
   "value": [
    0.449,
    0.529
   ],
   "shown": "about half as fast as around 1980",
   "from": "decline.py ratio_2020_25_to_1980_85, ratio_sv2025_to_1980_85"
  },
  "years_to_zero_at_16_nT_from_2025": {
   "value": 1834.4,
   "shown": "about 1,830 years, around AD 3860",
   "from": "decline.py years_to_zero_at_16_from_2025"
  },
  "pace_2015_20_and_2020_25_nT_per_year": {
   "value": [
    7.61,
    10.68
   ],
   "shown": "picked up since 2015–20, from 7.6 to 10.7 nT a year, with 12.6 forecast",
   "from": "decline.py five_year_rates (2015–2020, 2020–2025)"
  },
  "reaches_50_percent_AD": {
   "value": {
    "line_24": 2636.5,
    "line_16": 2942.2,
    "line_12.6": 3189.7,
    "exp_decay": 3376.3,
    "speed_up": 2280.3
   },
   "shown": "AD 2640, 2940, 3190, about 3380 and about 2280 (AD 2640–3190 on straight lines; not before about AD 2300)",
   "from": "decline.py straight_lines.*.year_50pct, exp_decay.year_50pct, speedup.year_50pct"
  },
  "reaches_5_percent_AD": {
   "value": {
    "line_24": 3186.8,
    "line_16": 3767.7,
    "line_12.6": 4237.9,
    "exp_decay": 7865.4,
    "speed_up": 2341.3
   },
   "shown": "AD 3200, 3800, 4200, about 7900 and about 2340",
   "from": "decline.py straight_lines.*.year_5pct, exp_decay.year_5pct, speedup.year_5pct"
  },
  "reaches_60_percent_AD": {
   "value": {
    "line_24": 2514.2,
    "line_16": 2758.8,
    "line_12.6": 2956.7,
    "exp_decay": 3020.9,
    "speed_up": 2259.8
   },
   "shown": "",
   "from": "decline.py *.year_60pct"
  },
  "exp_decay_percent_in_4500": {
   "value": 28.1,
   "shown": "28%",
   "from": "decline.py exp_decay.pct_at_4500"
  },
  "exp_decay_vs_line_lost_1840_2025_percent": {
   "value": [
    9.05,
    8.9
   ],
   "shown": "almost indistinguishable",
   "from": "decline.py exp_5pct_per_century_loss_over_185yr_pct"
  },
  "speed_up_doubling_time_years": {
   "value": 70.0,
   "shown": "70 years (our construct)",
   "from": "decline.py doubling_time.2_to_16"
  },
  "speed_up_percent_in_2045": {
   "value": 99.05,
   "shown": "99% of today’s strength",
   "from": "decline.py chart_series.exp_speedup_double_70yr"
  },
  "needed_to_halve_by_2045": {
   "value": {
    "rate_nT_per_yr": 733.8,
    "times_2025_30_forecast": 58.2,
    "times_fastest_five_year_pace_since_1945": 30.6,
    "speed_up_doubling_time_needed_years": 2.38
   },
   "shown": "about 730 nT a year, 58 times the 2025–30 forecast, about 30 times the fastest five-year pace since 1945",
   "from": "decline.py twenty_forties.2045.*_50pct, twenty_forties.speedup_doubling_time_to_reach_50pct_by_2045_yr"
  },
  "needed_to_reach_5_percent_by_2045": {
   "value": {
    "rate_to_5pct_nT_per_yr": 1394.1,
    "x_sv2025": 110.6,
    "x_fastest24": 58.1,
    "rate_to_zero_nT_per_yr": 1467.5
   },
   "shown": "about 1,400 nT a year, 110 times the 2025–30 forecast, nearly 60 times the fastest five-year pace since 1945",
   "from": "decline.py twenty_forties.2045"
  }
 },
 "experts": {
  "long_term_average_percent_of_today": {
   "value": 60,
   "shown": "about 60% (one study of Galápagos and Antarctic lavas) [10]",
   "from": "Wang, Kent and Rochette 2015"
  },
  "laschamp_low_percent_of_today": {
   "value": 5,
   "shown": "about 5%: Laschamp’s low in the LSMOD.2 model [18], as Larsen and colleagues compute it [6]",
   "from": "Korte et al. 2019 (LSMOD.2); Larsen et al. 2026 §3 (0.386 against 7.7 × 10^22 A m2)"
  },
  "half_strength_where_excursions_began_percent_of_today": {
   "value": 50,
   "shown": "half today’s strength, the level at which past excursions began [18][29]",
   "from": "Laj and Kissel 2015 (Laschamp’s directional changes start at about half the non-transitional value); Korte et al. 2019 §4.4 (about half the present-day field, 40 ZAm2)"
  },
  "no_excursion_or_reversal_expected_before_years": {
   "value": "500–1000",
   "shown": "the one such study that gives a timescale expects no excursion or reversal for 500 to 1,000 years [29]",
   "from": "Laj and Kissel 2015, abstract"
  },
  "excursions_since_last_reversal": {
   "value": {
    "listed": "12–17",
    "well_recorded": 7
   },
   "shown": "12 to 17, about 7 well recorded [14]",
   "from": "Channell 2012"
  },
  "our_catalog": {
   "value": {
    "events": 11,
    "years": 211000,
    "disputed": 4
   },
   "shown": "11 in the last 211,000 years, four of them disputed",
   "from": "the six recent events plus the five older ones above; the four disputed are Tianchi, Gothenburg, Hilina Pali and Rockall"
  },
  "odds_per_century_percent": {
   "value": {
    "7 in 780,000 years": 0.09,
    "12 in 780,000": 0.154,
    "17 in 780,000": 0.218,
    "11 in 211,000": 0.52
   },
   "shown": "roughly 0.1 to 0.5%",
   "from": "pattern.py poisson_percent_per_century"
  }
 }
}